全文获取类型
收费全文 | 7913篇 |
免费 | 509篇 |
国内免费 | 3篇 |
专业分类
8425篇 |
出版年
2022年 | 38篇 |
2021年 | 83篇 |
2020年 | 71篇 |
2019年 | 66篇 |
2018年 | 157篇 |
2017年 | 156篇 |
2016年 | 208篇 |
2015年 | 333篇 |
2014年 | 376篇 |
2013年 | 445篇 |
2012年 | 546篇 |
2011年 | 482篇 |
2010年 | 364篇 |
2009年 | 229篇 |
2008年 | 454篇 |
2007年 | 412篇 |
2006年 | 388篇 |
2005年 | 332篇 |
2004年 | 349篇 |
2003年 | 299篇 |
2002年 | 315篇 |
2001年 | 190篇 |
2000年 | 164篇 |
1999年 | 132篇 |
1998年 | 73篇 |
1997年 | 58篇 |
1996年 | 75篇 |
1995年 | 49篇 |
1994年 | 49篇 |
1993年 | 57篇 |
1992年 | 95篇 |
1991年 | 95篇 |
1990年 | 76篇 |
1989年 | 64篇 |
1988年 | 58篇 |
1987年 | 51篇 |
1986年 | 64篇 |
1985年 | 55篇 |
1984年 | 58篇 |
1983年 | 38篇 |
1982年 | 52篇 |
1981年 | 54篇 |
1980年 | 49篇 |
1979年 | 47篇 |
1978年 | 39篇 |
1977年 | 43篇 |
1976年 | 38篇 |
1975年 | 42篇 |
1974年 | 41篇 |
1973年 | 44篇 |
排序方式: 共有8425条查询结果,搜索用时 8 毫秒
11.
12.
The effect of hirudin and heparin on thrombin-induced consumption of antithrombin III, fibrinogen and platelets was studied in a rat model. Antithrombin III is consumed by tolerated thrombin doses by about 20 per cent. Hirudin and heparin ameliorate the consumption of fibrinogen and platelets at the low thrombin dose used. At high thrombin doses, tolerated only during simultaneous administration of exogenous inhibitors, heparin leads to markedly increased consumption of anti-thrombin III, whereas hirudin does not. With either kind of treatment, the thrombin effect on fibrinogen and platelets is inhibited, however, hirudin acts independently of a cofactor in contrast to heparin. 相似文献
13.
Sequence of the 5-aminolevulinic acid dehydratase-encoding gene from the hyperthermophilic methanogen, Methanothermus sociabilis. 总被引:2,自引:0,他引:2
We report on the sequence of the Methanothermus sociabilis aladh gene, which encodes the 5'-aminolevulinic acid dehydratase. The identity of the enzyme was determined by sequence comparison and by expression in Escherichia coli. 相似文献
14.
An endogenous ligand for the central sulfonylurea receptor 总被引:2,自引:0,他引:2
An endogenous ligand for the rat central sulfonylurea receptor has been evidenced in the rat central nervous system. The characteristics of this ligand (extractibility, non-dialysability, chromatographic behaviour on different media, sensitivity to proteases) indicate that it is a neutral to slightly basic peptide. 相似文献
15.
Serum steroid levels in intact and endocrine ablated BALB/c nude mice and their intact littermates 总被引:2,自引:0,他引:2
N Brünner B Svenstrup M Spang-Thomsen P Bennett A Nielsen J Nielsen 《Journal of steroid biochemistry》1986,25(3):429-432
An investigation was made of the serum steroid levels found in intact and endocrine ablated nude mice of both sexes and in their intact homozygous littermates. The results showed that nude mice have a normal steroidogenesis, but with decreased levels of circulating steroids compared to those of the littermates. The efficacy of the endocrine ablations was confirmed by the reduction in serum oestrone following oophorectomy, and by the reduction in serum testosterone and progesterone following orchiectomy. The normal steroidogenesis in nude mice, and the similarities between mouse and man with regard to changes in serum steroids following oophorectomy and orchiectomy, support the usefulness of human tumor xenograft models for the study of hormone-tumor interactions. 相似文献
16.
A prospective controlled investigation in 134 consecutive outpatients compared the cytologic adequacy of sputum samples obtained by spontaneous and provoked expectoration. Inhalation of nebulized 10% sodium chloride was used for provoked expectoration. A significantly higher number of adequate samples was produced after provocation, as judged by the presence of alveolar macrophages (X2 = 5.63; p less than 0.02). The improvement in sample adequacy was limited to the nonsmokers and ex-smokers in the study. This result, together with the relatively high cost of cytologic sputum examinations, indicates that provoked expectoration should at least be applied to the collection of sputum samples from nonsmokers and ex-smokers. 相似文献
17.
The different types of recrystallization which can be observed in the Triassic involutinids should be considered in the taxonomic treatment of this foraminiferal family. If the diagenetic modifications of the test are neglected the same form could be placed into different suborders. Our inclusion of the genusTriasina Majzon in the Involutinidae proposed earlier on purely morphologic grounds, seems to be supported by the fact that the same types of recrystallization exist inTrocholina, Involutina undTriasina. 相似文献
18.
19.
20.
Summary The feasibility of determining the relative populations of multi-conformer structures from NOE-derived distances alone is assessed. Without cross-validation of the NOE restraints, any population ratio can be refined to a similar quality of the fit. Complete cross-validation provides a less biased measure of fit and allows the estimation of the correct population ratio when used in conjunction with very tight distance restraints. With the qualitative distance restraints most commonly used in NMR structure determination, cross-validation is unsuccessful in providing the correct answer. Other experimental sources are therefore needed to determine relative populations of multi-conformer structures.To whom correspondence should be addressed. 相似文献