全文获取类型
收费全文 | 5459篇 |
免费 | 352篇 |
国内免费 | 4篇 |
出版年
2021年 | 108篇 |
2020年 | 73篇 |
2019年 | 74篇 |
2018年 | 126篇 |
2017年 | 93篇 |
2016年 | 137篇 |
2015年 | 227篇 |
2014年 | 213篇 |
2013年 | 302篇 |
2012年 | 341篇 |
2011年 | 358篇 |
2010年 | 208篇 |
2009年 | 176篇 |
2008年 | 251篇 |
2007年 | 288篇 |
2006年 | 248篇 |
2005年 | 227篇 |
2004年 | 216篇 |
2003年 | 195篇 |
2002年 | 184篇 |
2001年 | 79篇 |
2000年 | 64篇 |
1999年 | 64篇 |
1998年 | 53篇 |
1997年 | 46篇 |
1996年 | 49篇 |
1995年 | 37篇 |
1994年 | 41篇 |
1993年 | 43篇 |
1992年 | 55篇 |
1991年 | 58篇 |
1990年 | 54篇 |
1989年 | 41篇 |
1988年 | 54篇 |
1987年 | 47篇 |
1986年 | 58篇 |
1985年 | 51篇 |
1984年 | 49篇 |
1983年 | 37篇 |
1982年 | 37篇 |
1981年 | 38篇 |
1979年 | 36篇 |
1978年 | 40篇 |
1977年 | 43篇 |
1976年 | 36篇 |
1975年 | 35篇 |
1974年 | 39篇 |
1973年 | 37篇 |
1972年 | 32篇 |
1971年 | 30篇 |
排序方式: 共有5815条查询结果,搜索用时 14 毫秒
1.
2.
3.
Pfarrer Ch. Münch 《Plant Systematics and Evolution》1862,12(2):35-37
Ohne Zusammenfassung 相似文献
4.
Bacopa monniera Wettst. (BM, syn. Herpestis monniera L; Scrophulariaceae), is an Ayurvedic drug used as a rasayana. Its fresh juice was earlier reported to have significant antiulcerogenic activity. In continuation, methanolic extract of BM (BME) standardized to bacoside-A content (percentage-38.0 ± 0.9), when given in the dose of 10–50 mg/kg, twice daily for 5 days, showed dose-dependent anti-ulcerogenic on various gastric ulcer models induced by ethanol, aspirin, 2 h cold restraint stress and 4 h pylorus ligation. BME in the dose of 20 mg/kg, given for 10 days, twice daily showed healing effects against 50% acetic acid-induced gastric ulcers. Further work was done to investigate the possible mechanisms of its action by studying its effect on various mucosal offensive acid-pepsin secretion and defensive factors like mucin secretion, mucosal cell shedding, cell proliferation and antioxidant activity in rats. BME 20 mg/kg showed no effect on acid-pepsin secretion, increased mucin secretion, while it decreased cell shedding with no effect on cell proliferation. BME showed significant antioxidant effect per se and in stressed animals. Thus, the gastric prophylactic and curative effects of BME may be due to its predominant effect on mucosal defensive factors. 相似文献
5.
K. Sasikala Ch.V. Ramana P. Raghuveer Rao M. Subrahmanyam 《FEMS microbiology letters》1990,72(1-2):23-28
Abstract Photoproduction of hydrogen, nitrogenase activity (acetylene reduction) and hydrogenase activity (methylene blue dye reduction) were studied in free and alginate immobilized whole cells of a purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides O.U. 001. Four-fold increase in hydrogen production, two-fold increase in nitrogenase activity and 1.2-fold increase in the hydrogenase activity were observed in immobilized cells compared to free cells. Effect of various inhibitors (CO and C2 H2 ) and electron donor (H2 ) on the above three functions by free and immobilized cells has also been studied. 相似文献
6.
Digital images of ex situ germplasm stored in the Sardinian Germplasm Bank (BG-SAR) were used for the application of image analysis techniques at the Stazione Sperimentale di Granicoltura per la Sicilia. The analysed accessions refer to 148 taxonomic units belonging to 102 genera and 47 families, typical of the Sardinian flora, and of the Mediterranean basin in general.The images of diaspores were acquired by a flatbed scanner and elaborated with a macro specially developed for the morphometric and colorimetric measurements. This method allowed carrying out a database for the characterization of autochthonous germplasm in entry to the bank and the realization of statistic classifiers for the discrimination of genera and species within the following families: Apiaceae, Boraginaceae, Caryophyllaceae, Cistaceae, Fabaceae and Scrophulariaceae. Such classifiers, based on the linear discriminant analysis (LDA) technique and checked by cross-validation, showed a performance included between 74.3% and 96.4%.In addition, for the genus Astragalus, it was possible to elaborate a classifier able to identify very similar taxa of a species complex, obtaining a performance between 83.7% and 100%. Such analysis proved the validity of the methodology also from the taxonomic point of view.Suggestions for subsequent methodological progress, which could offer applications in other research issues, such as ecological analysis, soil seed bank and archaeological botany are proposed. 相似文献
7.
Mesophyll derived protoplasts ofCatharanthus roseus cv. Little pinkie were fused with protoplasts derived from an habituated cell line ofC. roseus. Polyethylene glycol was used as agglutinating agent while fusions were induced by square pulses. Best results were obtained
by fusing protoplasts from primary leaves with those from three-day-old cell cultures. Adding calcium ions considerably enhanced
heterofusion rate. Good cell viabilities indicated that this fusion process was not cytotoxic. The heterofusion frequency
was up to 10% or more. Most of the heterokaryons were able to regenerate their cell walls and underwent division.
Communicated by J. TUPY 相似文献
8.
9.
10.
Oscar Fernandez‐Capetillo 《EMBO reports》2010,11(1):32-36
Ageing is an unavoidable corollary to being alive; the most intuitive interpretation of ageing being that it is the consequence of progressive body degeneration. In agreement with this, current models propose that ageing occurs through a stepwise accumulation of DNA damage, which ultimately limits the regenerative capacity of tissues. On the other hand, there is increasing evidence that fetal distress can influence the development of disease in adult life, a phenomenon known as ‘intrauterine programming’. The extent to which an intrauterine exposure to DNA damage can compromise lifespan remains unclear. My group has recently generated a murine model of a human syndrome linked to defective DNA repair and observed that these animals age prematurely, but the accumulation of DNA damage is restricted mostly to the embryonic period. Here, I discuss the implications of this finding and propose that ageing can be influenced by fetal distress. 相似文献