全文获取类型
收费全文 | 1045篇 |
免费 | 1篇 |
专业分类
安全科学 | 18篇 |
废物处理 | 2篇 |
环保管理 | 86篇 |
综合类 | 824篇 |
基础理论 | 67篇 |
污染及防治 | 36篇 |
评价与监测 | 8篇 |
社会与环境 | 2篇 |
灾害及防治 | 3篇 |
出版年
2021年 | 4篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 39篇 |
2012年 | 6篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 10篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1997年 | 4篇 |
1995年 | 56篇 |
1994年 | 50篇 |
1993年 | 38篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 4篇 |
1973年 | 10篇 |
1971年 | 4篇 |
1962年 | 3篇 |
1961年 | 4篇 |
1950年 | 3篇 |
1919年 | 47篇 |
1918年 | 44篇 |
1917年 | 36篇 |
1916年 | 54篇 |
1915年 | 37篇 |
1914年 | 71篇 |
1913年 | 107篇 |
排序方式: 共有1046条查询结果,搜索用时 31 毫秒
641.
Martin?HeilEmail author Birgit?Baumann Ralf?Krüger K. Eduard?Linsenmair 《Chemoecology》2004,14(1):45-52
Summary. Myrmecophytic plants use obligate ant mutualists as a constitutive
indirect defence mechanism. These plants often produce cellular food bodies (FBs) to
nourish their resident ants. Lipids, proteins, and even highly specialised compounds
such as glycogen have been reported from FBs, but detailed chemical analyses of FB
composition have so far been presented only for Southeast Asian Macaranga
and Central American Piper myrmecophytes. Here we
report the chemical composition of FBs of five myrmecophytic Acacia
(Fabaceae) species from Mexico using HPLC (carbohydrates and proteins) and GC-MS
(lipids). Feeding experiments revealed no hints on any use of external food sources
by the inhabiting Pseudomyrmex ants. These ants
obviously rely completely on FBs and extrafloral nectar provided by their hosts.
The total content of nutrients in Acacia FBs was 15-25% of FB
dry mass, being much lower than in Macaranga or
Piper FBs. Proteins were dominating (8-14 % dm)
in Acacia FBs and thus were present in higher amounts than in
Macaranga FBs, yet in lower amounts than in
Piper. Lipids contributed 1-9 %
of dry mass, showing a lower proportion than in FBs of Macaranga
or Piper. Carbohydrates made up 3-11 % dm, reaching
in most Acacia species the same range as observed in
Macaranga and in Piper FBs.
Water content was 18-24 % of FB fresh mass, and structural tissue obviously made up
a much higher proportion in Acacia FBs than in
Macaranga or Piper
FBs. Both characters might represent an adaptation to producing FBs unprotected at
the leaf tips under dry conditions. Acacia FBs
contain all amino acids and all fatty acids that are considered essential for
insects, and their contents of lipids and proteins are higher than in the leaves
from which they are ontogenetically derived. This indicates a putatively adaptive
enrichment of nutritionally valuable compounds in structures functioning as ant-food. 相似文献
642.
Simpson—Golabi—Behmel (SGB) syndrome is an X-linked condition with pre- and postnatal overgrowth, characteristic facies, and visceral and skeletal anomalies. We report an affected male who presented at 16 weeks' gestation with elevated maternal serum α-fetoprotein (MSAFP). Fetal measurements at 20 and 31 weeks' gestation were disproportionate, with marked macrosomia but a low head to abdominal circumference ratio and normal femur length. Fetal overgrowth with elevated MSAFP may prove to be useful markers for the prenatal diagnosis of SGB syndrome. 相似文献
643.
Dr. Lilian M. Lopes Sang Choon Cha Edécio Armbruster De Moraes Marcelo Zugaib 《黑龙江环境通报》1995,15(2):183-185
Fetal echocardiography was performed during the third trimester in a normal primigravida. The fetal heart was severely affected with the typical cardiac manifestations of Marfan syndrome. The medical history of the father was investigated and a mild form of the syndrome was diagnosed. The neonate died at 2 months of age of congestive heart failure. 相似文献
644.
A case of prenatal diagnosis of the Pierre Robin sequence is reported in which hydramnios and amniotic bands are present. The possible pathogenesis is discussed. 相似文献
645.
Fibrinopeptide levels were measured in 20 women during transcervical chorionic villus sampling (CVS). Fibrinopeptide A, a sensitive indicator of fibrinogen cleavage by thrombin, significantly increased in five subjects, whereas there was no change in Bβ peptide, an indicator of fibrinolysis. The data suggest that modest fibrin formation, uncompensated by fibrinolysis, may be induced in some women by CVS. 相似文献
646.
Dr O. P. Van Diggelen H. Von Koskull P. Ämmälä G. T. M. Vredeveldt H. C. Janse W. J. Kleijer 《黑龙江环境通报》1988,8(9):661-663
Wolman's disease was diagnosed in the first trimester of pregnancy by the direct demonstration of acid lipase deficiency in chorionic villi. The diagnosis was confirmed by studies on cultured chorionic villus cells and fetal skin fibroblasts. Acid lipase activity was assayed with both 4-methylumbelliferyl-palmitate and radiolabelled cholesterol oleate as substrates. The higher specificity of the enzyme for the latter, natural, substrate makes it superior in prenatal diagnosis. 相似文献
647.
In the period of a retrospective study (1979–1984 inclusive) forty cases of sex chromosome aneuploidy were identified at amniocentesis in Oxford, England and in Kuopio, Finland; 25 of these pregnancies were subsequently terminated. A decision to continue was made more often for XYY and XXX karyotypes, by older mothers and older fathers, by couples with more previous children, and by couples living in England. A decision to terminate was made more often for XXY and non-mosaic 45,X karyotypes, by younger mothers and younger fathers, by couples with few previous children, in all cases with abnormal ultrasound findings, when post-amniocentesis counselling was given by an obstetrician, and by couples living in Finland. Previous miscarriages, or terminations of pregnancy, previous problems with infertility, marital status, or the type of counselling given before amniocentesis, appeared not to influence a couples' decision. Religious and ethical ideas were not studied systematically at the time and cannot be reported on. 相似文献
648.
A continuous wave Doppler unit was used to obtain umbilical and uterine artery flow velocity waveforms in pregnancies complicated by a major fetal abnormality. A total of 139 examinations were performed on 32 women between 26 to 41 weeks' gestation, and the records were reviewed to determine the changes associated with fetal malformation. The systolic/diastolic (A/B) ratio was used as an index of blood flow resistance in the umbilical artery and the systolic minus diastolic divided by systolic (A–B)/A for the branches of the uterine artery. Seventeen out of 32 patients showed high systolic/diastolic ratio in waveforms taken from the umbilical artery. In 30 out of 32 patients the uterine artery waveform was normal (in two patients the results were equivocal). It appears that a fetal mechanism may determine the changes in the umbilical placental circulation resulting in an umbilical artery pattern of high flow resistance in more than half of the patients with congenital anomalies. 相似文献
649.
Six cases are reported with discrepancies between the karyotypes of placental cells and cells from other fetal tissue. The respective findings were: (a) 48,+7,+18 resp. 47,+18. (b) 46, i(18q) resp. 46, del18(p11). (c) 46, XX resp. 46, XX/47, XXX. (d) 46, X, Yq+ and 46, XY resp. 46, XY. (e) 46/47,+12 resp. 46. (f) 46/47,+5 resp. 46. These differences were found in both early and term pregnancies. Care should be taken in deducing the fetal karyotype from the chromosomal pattern of placental cells. 相似文献
650.
Prenatal diagnosis of del(11)(p13p15) was made on cultured amniotic fluid cells and confirmed on fetal skin fibroblasts after termination of pregnancy. Both irides appeared behind schedule in development by 2–3 weeks in reference to the gestational age of the fetus. It is suggested that the aniridia of the aniridia-Wilms tumour association is due to developmental arrest. Confirmation of this complex is difficult at mid-gestation without critical pathological study of the eyes. 相似文献