全文获取类型
收费全文 | 2884篇 |
免费 | 266篇 |
国内免费 | 138篇 |
专业分类
3288篇 |
出版年
2023年 | 25篇 |
2022年 | 70篇 |
2021年 | 82篇 |
2020年 | 68篇 |
2019年 | 76篇 |
2018年 | 99篇 |
2017年 | 81篇 |
2016年 | 101篇 |
2015年 | 109篇 |
2014年 | 119篇 |
2013年 | 158篇 |
2012年 | 175篇 |
2011年 | 189篇 |
2010年 | 133篇 |
2009年 | 102篇 |
2008年 | 144篇 |
2007年 | 129篇 |
2006年 | 117篇 |
2005年 | 96篇 |
2004年 | 87篇 |
2003年 | 80篇 |
2002年 | 92篇 |
2001年 | 63篇 |
2000年 | 62篇 |
1999年 | 51篇 |
1998年 | 32篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1994年 | 14篇 |
1992年 | 48篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 28篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 33篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 34篇 |
1977年 | 22篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 14篇 |
1973年 | 19篇 |
1969年 | 14篇 |
排序方式: 共有3288条查询结果,搜索用时 15 毫秒
941.
P K Adhikary S K Sen M A Maleque 《Biochemical and biophysical research communications》1990,170(2):448-455
Pyridino [1,2-a] imidazo [5,4-b] indole (Compound 1) has been reported previously as an antihypertensive agent. Parenteral introductions of Compound 1 in spontaneously hypertensive rats (SHR) and in normotensive dogs have been found to reduce systolic blood pressure (SBP) in those animal models. Later studies have shown cholinomimetic effects of Compound 1 in animal tissue preparations and in live animals. Our experiments showed that daily oral administration of Compound 1 minimized the development of hypertensive nephrosclerosis and prevented premature death in male SHR. Compound 1 also potentiated cholinergic activity in isolated rabbit hearts. It is suggested that cholinergic vasodilation by Compound 1 is responsible for the hypotensive effect and prevention of nephrosclerosis in SHR. 相似文献
942.
The effect of Ficoll 70 on the thermal stability and structure of creatine kinase (CK) was studied using far-UV CD spectra
and intrinsic fluorescence spectra. The thermal transition curves monitored by CD spectra were fitted to a two-state model
using a modified form of the van’t Hoff equation to obtain the transition temperature (T
m) and enthalpy change (ΔH
u) of thermally induced denaturation of CK in the absence and presence of Ficoll 70. An increase in T
m with constant ΔH
u was observed with increasing Ficoll 70 concentration, suggesting that Ficoll 70 enhances the thermal stability of CK. Fluorescence
spectral measurements confirmed this protective effect of Ficoll 70 on CK structure. In addition, we observed a crowding-induced
compaction effect on the structure of both native state and thermally denatured state of CK in the presence of Ficoll 70,
which is more obvious on the structure of the denatured ensemble compared to that of the native ensemble. Our observations
qualitatively accord with the predictions of previously proposed crowding theory for the effect of intermolecular excluded
volume on protein stability and structure. These findings imply that the effects of macromolecular crowding are essential
to our understanding of protein folding and unfolding occurring in vivo. 相似文献
943.
944.
945.
The activity of NAD+-dependent PGDH was measured in the cytosolic fractions (100,000 x g) of uterine tissues obtained from transsexual, pregnant and non-pregnant women. The specific activity (mean +/- SD) of the enzyme at maximum velocity of the enzyme reaction in these three groups of women was 5.5 +/- 2.30, 0.53 +/- 0.27 and 0.54 +/- 0.25 mU/mg protein respectively using PGE2 as substrate, and with PGF2 alpha as substrate the respective values were 5.48 +/- 2.80, 0.49 +/- 0.41 and 0.51 +/- 0.30 mU/mg protein. These data suggest that, with either substrate, the uterine enzyme activity in the transsexuals was about 10-fold greater than in pregnant and non-pregnant women (p less than 0.001). However, the Km values of the enzyme for both PGE2 and PGF2 alpha were similar in all three groups, indicating the presence of same enzyme in the uterus of transsexual, pregnant and non-pregnant women. We speculate that PGDH activity was raised in the uterus of transsexual women because of the prolonged androgen therapy they received for the management of female-to-male transsexualism. 相似文献
946.
Pali Sen 《Biometrical journal. Biometrische Zeitschrift》1989,31(8):973-992
The molecular biology of transformed cancer cells singles out key enzymes as sensitive targets of anti-cancer drugs. Here we use one substrate–one intermediate–one final product model for a coupled enzyme system. The transfer rates for the mechanism are taken as continuous but subject to random fluctuations. Explicit formulae for the first moments of the distribution of the process are obtained. These formulae allow us to take into account not only the variability between the subjects, but also the variability of the process for a single subject. The present results allow us also to build the prediction interval for a particular time period given the observations for some preceding moments. 相似文献
947.
948.
Summary The beneficial effect of spraying some highly active phyllosphere N2-fixing microorganisms on high and low yielding cultivars of rice plants as compared with that of urea applied at different
doses are described. The dry weight, N-content, 1000 grain weight, and yield were remarkably increased in all cases with the
application of phyllosphere microorganisms. The performance of two isolates KUP4 and KUPBR2 with IR-8 and IR-26 rice, was better than that of 52 kg urea-N per hectare. IR-579 rice leaves in association with some phyllosphere
bacteria reduced acetylene at the rate of 664–816 nmoles/g leaf/h. In IR-26 rice the effect of application of bacterial suspension
at three phases of plant growth corresponded very well with that of urea application in three split doses under identical
conditions. Recommended fertilizer rates produced the same yield as the half dose plus bacterial spray in the cultivars Pankaj
and Rupsail. Fertilizer application in Pankaj and Rupsail rice reduced nitrogenase activity and the beneficial effects of
phyllosphere N2-fixation was reduced by 40–55%. 相似文献
949.
950.