全文获取类型
收费全文 | 9117篇 |
免费 | 1010篇 |
国内免费 | 3篇 |
出版年
2021年 | 129篇 |
2020年 | 84篇 |
2019年 | 93篇 |
2018年 | 138篇 |
2017年 | 137篇 |
2016年 | 204篇 |
2015年 | 339篇 |
2014年 | 357篇 |
2013年 | 488篇 |
2012年 | 567篇 |
2011年 | 559篇 |
2010年 | 357篇 |
2009年 | 364篇 |
2008年 | 517篇 |
2007年 | 445篇 |
2006年 | 401篇 |
2005年 | 436篇 |
2004年 | 413篇 |
2003年 | 434篇 |
2002年 | 359篇 |
2001年 | 153篇 |
2000年 | 122篇 |
1999年 | 153篇 |
1998年 | 138篇 |
1997年 | 106篇 |
1996年 | 107篇 |
1995年 | 89篇 |
1994年 | 95篇 |
1993年 | 89篇 |
1992年 | 96篇 |
1991年 | 93篇 |
1990年 | 80篇 |
1989年 | 89篇 |
1988年 | 87篇 |
1987年 | 92篇 |
1986年 | 95篇 |
1985年 | 104篇 |
1984年 | 83篇 |
1983年 | 90篇 |
1982年 | 88篇 |
1981年 | 88篇 |
1980年 | 74篇 |
1979年 | 73篇 |
1978年 | 65篇 |
1977年 | 73篇 |
1976年 | 57篇 |
1975年 | 57篇 |
1974年 | 50篇 |
1972年 | 56篇 |
1969年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
F. H. Dawson 《Hydrobiologia》1981,77(1):71-76
The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards. 相似文献
3.
N. L. Biddington P. A. Brocklehurst A. S. Dearman Jane Dearman 《Physiologia plantarum》1982,55(4):407-410
Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
4.
A. J. Edwards J. D. Hamilton W. D. Nichol G. W. Taylor A. M. Dawson 《BMJ (Clinical research ed.)》1970,1(5692):342-345
Seven patients with “coeliac axis compression syndrome” are reported. Five were treated surgically, but only two did well. A survey of 200 healthy adults showed epigastric bruits in 6·5%; only one of these had dyspepsia, though dyspepsia was present in 12·5% overall.Caution is urged in attributing a causal relationship between coeliac axis compression and pain and in proceeding to arteriography when compression is suspected on clinical grounds. 相似文献
5.
6.
Pairs of radioimmunoassays, each of which include a two-dimensional matrix of standards, have been previously employed to resolve specificity problems in steroid immunoassay. In this study the bivariate radioimmunoassay principle has been applied to simultaneous measurement of plasma antidiuretic hormone, arginine vasopressin, and the synthetic antidiuretic agent 1-deamino-8-D-arginine vasopressin (desmopressin), by utilizing two arginine vasopressin antisera which show significantly different cross-reactivities with the synthetic analog. Data processing consists of mathematical representation of two curved dose-response surfaces followed by solution of this pair of nonlinear simultaneous equations for the unknown arginine vasopressin and desmopressin concentrations. Details of numerical procedures are given in the Appendix. The assay appears entirely adequate in terms of sensitivity, accuracy, and precision for measurement of these antidiuretic agents in clinical samples. No evidence of significant covariance in estimated concentrations could be detected but precision of estimation is (not unexpectedly) a function of the concentration of both agents. The plasma disappearance half-time of desmopressin (probably the second of a biphasic disappearance) was estimated as 37 min in one normal subject, which is in good agreement with a previously reported value of 30 min. 相似文献
8.
9.
10.