全文获取类型
收费全文 | 18027篇 |
免费 | 296篇 |
国内免费 | 538篇 |
专业分类
安全科学 | 650篇 |
废物处理 | 770篇 |
环保管理 | 2630篇 |
综合类 | 3264篇 |
基础理论 | 4554篇 |
环境理论 | 7篇 |
污染及防治 | 4799篇 |
评价与监测 | 1006篇 |
社会与环境 | 1031篇 |
灾害及防治 | 150篇 |
出版年
2023年 | 101篇 |
2022年 | 193篇 |
2021年 | 190篇 |
2020年 | 199篇 |
2019年 | 164篇 |
2018年 | 303篇 |
2017年 | 289篇 |
2016年 | 429篇 |
2015年 | 372篇 |
2014年 | 474篇 |
2013年 | 1470篇 |
2012年 | 659篇 |
2011年 | 923篇 |
2010年 | 707篇 |
2009年 | 791篇 |
2008年 | 860篇 |
2007年 | 896篇 |
2006年 | 755篇 |
2005年 | 636篇 |
2004年 | 631篇 |
2003年 | 581篇 |
2002年 | 556篇 |
2001年 | 663篇 |
2000年 | 541篇 |
1999年 | 326篇 |
1998年 | 224篇 |
1997年 | 239篇 |
1996年 | 229篇 |
1995年 | 273篇 |
1994年 | 219篇 |
1993年 | 213篇 |
1992年 | 176篇 |
1991年 | 183篇 |
1990年 | 183篇 |
1989年 | 181篇 |
1988年 | 153篇 |
1987年 | 133篇 |
1986年 | 158篇 |
1985年 | 143篇 |
1984年 | 191篇 |
1983年 | 147篇 |
1982年 | 172篇 |
1981年 | 159篇 |
1980年 | 130篇 |
1979年 | 150篇 |
1978年 | 94篇 |
1977年 | 98篇 |
1975年 | 88篇 |
1974年 | 93篇 |
1972年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
Maternal serum alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (βhCG) measurements taken prior to chorionic villus sampling (CVS) in 21 patients who subsequently miscarried were compared with measurements in a control group of 113 patients with uneventful pregnancies. Patients with AFP levels of 10 iu/ml or more prior to the CVS had a 4·3 times greater risk of miscarriage (95 per cent confidence interval 1·3–13·6). AFP levels obtained 1 week after the CVS in the 13 patients with late miscarriages were higher than in the control group (P = 0·06). Patients miscarrying had a greater rise in AFP (P = 0·06) and a greater fall in βhCG levels (P = 0·04) following the CVS procedure, compared with the control subjects. Each 10-unit change in the difference between AFP or βhCG levels prior to and 1 week following the CVS was associated with a significantly increased risk for late miscarriage. Elevated maternal serum AFP levels early in pregnancy and changes in AFP and βhCG levels following CVS may predict an increased risk for subsequent miscarriage. 相似文献
252.
253.
254.
255.
256.
257.
258.
259.
Uterine lavage affords the potential for non-invasive human blastocyst recovery, with obvious potential for preimplantation genetic diagnosis. In an effort to duplicate in women the multiple blastocyst recovery per cycle that can be achieved in several other species, we initiated a programme in which fertile women underwent superovulation, followed by lavage and embryo collection. We superovulated 15 fertile women, aged 21–40, in 29 cycles using one of four regimens. Insemination was by either intercourse or artificial intracervical donor insemination with cryopreserved sperm from men of proven fertility. In 28 of 29 cycles, the uterus was lavaged daily for 1, 2, or 3 days between 5 and 10 days after human chorionic gonadotropin (hCG) administration or luteinizing hormone (LH) surge. Almost total fluid volume was recovered in every lavage. There were no retained pregnancies and no complications. Surprisingly, only two morulae, one blastocyst, and four unfertilized ova were recovered. Thus, alterations in ovulation induction, insemination timing, or lavage techniques must be contemplated in order to increase the blastocyst yield and thus fulfil the potential of uterine lavage for preimplantation diagnosis. 相似文献
260.
We are very grateful to A. Gessner for his great help in the construction of the apparatus and A. Meyer for performance of some pressure bomb experiments. This work was supported by grants of the Deutsche Forschungsgemeinschaft (Forschergruppe Ökophysiologie) to U.Z. and O.L.L. 相似文献