全文获取类型
收费全文 | 474415篇 |
免费 | 58685篇 |
国内免费 | 286篇 |
专业分类
533386篇 |
出版年
2018年 | 4127篇 |
2017年 | 3805篇 |
2016年 | 5972篇 |
2015年 | 8984篇 |
2014年 | 10076篇 |
2013年 | 13979篇 |
2012年 | 16202篇 |
2011年 | 16174篇 |
2010年 | 10687篇 |
2009年 | 9880篇 |
2008年 | 14167篇 |
2007年 | 14533篇 |
2006年 | 13198篇 |
2005年 | 12974篇 |
2004年 | 12708篇 |
2003年 | 12121篇 |
2002年 | 11633篇 |
2001年 | 22236篇 |
2000年 | 22375篇 |
1999年 | 17905篇 |
1998年 | 6540篇 |
1997年 | 6773篇 |
1996年 | 6558篇 |
1995年 | 5949篇 |
1994年 | 5990篇 |
1993年 | 5835篇 |
1992年 | 14120篇 |
1991年 | 13380篇 |
1990年 | 13064篇 |
1989年 | 12966篇 |
1988年 | 11545篇 |
1987年 | 11201篇 |
1986年 | 10190篇 |
1985年 | 10047篇 |
1984年 | 8526篇 |
1983年 | 7352篇 |
1982年 | 5816篇 |
1981年 | 5273篇 |
1980年 | 4888篇 |
1979年 | 8000篇 |
1978年 | 6187篇 |
1977年 | 5659篇 |
1976年 | 5288篇 |
1975年 | 5604篇 |
1974年 | 6088篇 |
1973年 | 5925篇 |
1972年 | 5325篇 |
1971年 | 4942篇 |
1970年 | 4110篇 |
1969年 | 4049篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Antileukoprotease (ALP) was isolated from bronchial secretion. The amino acid composition as well as the N-terminal sequence were determined. No homology with other low molecular weight proteinase inhibitors was found. 相似文献
993.
Monocytes are known to produce both hematopoietic growth factors and other factors, monokines, which do not directly stimulate hematopoiesis. Monokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) may indirectly stimulate mesenchymal cells to produce hematopoietic growth factors. The identity of all the factors produced by monocytes or mesenchymal cells has not been established because of overlapping activities on biologic assay. The purpose of this study was to identify the individual growth factors produced by endothelial cells before and after stimulation with various monokines. We prepared conditioned media and extracted RNA from endothelial cells before and after stimulation with monokines. The results show that immortalized endothelial cells produce maximal detectable amounts of granulocyte-macrophage colony-stimulating factor (GM-CSF) constitutively. In contrast, GM-CSF production by primary endothelial cells requires induction with either IL-1 or TNF. 相似文献
994.
In phenotype the mycoplasmas are very different from ordinary bacteria. However, genotypically (i.e., phylogenetically) they are not. On the basis of ribosomal RNA homologies the mycoplasmas belong with the clostridia, and indeed have specific clostridial relatives. Mycoplasmas are, however, unlike almost all other bacteria in the evolutionary characteristics of their ribosomal RNAs. These RNAs contain relatively few of the highly conserved oligonucleotide sequences characteristic of normal eubacterial ribosomal RNAs. This is interpreted to be a reflection of an elevated mutation rate in mycoplasma lines of descent. A general consequence of this would be that the variation associated with a mycoplasma population is augmented both in number and kind, which in turn would lead to an unusual evolutionary course, one unique in all respects. Mycoplasmas, then, are actually tachytelic bacteria. The unusual evolutionary characteristics of their ribosomal RNAs are the imprints of their rapid evolution. 相似文献
995.
Energy-induced modulation of the kinetics of oxidative phosphorylation and reverse electron transfer
The kinetics of ATP synthesis by bovine heart submitochondrial particles (SMP) are modulated by the rate of energy production by the respiratory chain between two fixed limits characterized by apparent KmADP = 2-4 microM and Vmax approximately 200 nmol of ATP min-1 (mg of SMP protein)-1 at low energy levels and apparent KmADP = 120-160 microM and Vmax = 11,000 nmol of ATP min-1 (mg of SMP protein)-1 at high energy levels. These data indicate that KmADP and Vmax increase approximately 50-fold each; therefore, there is essentially no change in the catalytic efficiency of the ATP synthase complex in going from one extreme to the other. At intermediate rates of energy production, the kinetic data required introduction of a third, intermediate KmADP. A KmADP of 10-15 microM fitted all the data reported here and previously [Matsuno-Yagi, A., & Hatefi, Y. (1986) J. Biol. Chem. 261, 14031-14038]. However, this is not meant to suggest that there is a fixed intermediate KmADP, as the transition from one fixed limit to the other may be fluid or involve more than one intermediate state. In addition, it has been shown that kinetic plots of SMP-catalyzed and ATP-driven reverse electron transfer from succinate to NAD are curvilinear and resolvable into a minimum of two apparent KmNAD values of about 20-30 and 200-300 microM. These results have been discussed in relation to the three potentially active catalytic sites of F1-ATPase and the structure of the NADH:ubiquinone oxidoreductase complex, the curvilinear kinetics of ATP hydrolysis, and changes in KmADP and KmPi in photophosphorylation as affected by the duration and intensity of light. 相似文献
996.
997.
A spectroscopic analysis of the thermally induced folding-unfolding transition of beta-trypsin. 下载免费PDF全文
Absorption and fluorescence changes were used to monitor the thermally induced folding-unfolding transition of beta-trypsin. These parameters reflect changes in the microenvironment of different subsets of the four tryptophanyl residues of this protein. The thermal transition was found to be sequential. 相似文献
998.
Kathryn M. Denkowski George C. Denkowski 《Applied psychophysiology and biofeedback》1984,9(3):353-364
This study examined whether group progressive relaxation training was as effective as individual EMG biofeedback training in facilitating the academic achievement and self-control of 45 hyperactive elementary school children. Academic achievement was assessed with the Gates-MacGinities Reading Tests, and self-control was measured with the Nowicki-Strickland and the Teacher Rating scales. Eight sessions were scheduled at weekly intervals. Progressive relaxation was conducted in groups of seven or eight and was induced with a commercial audiocassette program. EMG training augmented frontalis biofeedback with those taped exercises. A placebo group listened to taped children's stories. Multivariate analysis of variance indicated no significant differences among the three contrast groups when all dependent variables were considered together. However, univariate F values and discriminant analysis disclosed locus of control to be significantly more internal for the progressive relaxation condition. Also, differences between the two relaxation and the placebo groups, though not statistically significant, were all in the expected direction. While the relative efficacy of group progressive relaxation could not be established conclusively, the data appeared sufficiently positive to warrant further investigation of this cost-effective prospective intervention.The opinions expressed by the authors are not necessarily those of their respective institutions. 相似文献
999.
M T Hsieh H C Chen P H Hsu T Shibuya 《Proceedings of the National Science Council, Republic of China. Part B, Life sciences》1986,10(1):43-48
Previously, it was found that the ancient Chinese remedy of Suanzaorentang could be a promising anxiolytic drug (Chen and Hsieh, 1985a, Chen and Hsieh, 1985b). To understand the mechanism of the action of Suanzaorentang, the effects of Suanzaorentang on behavior changes and central monoamines and their metabolites were studied in rats. It was found that Suanzaorentang significantly (1) prolonged the period from the onset of clonic to tonic convulsions induced by pentylenetetrazol or picrotoxin, (2) prolonged the sleep duration induced by hexobarbital, (3) reduced locomotor activity, (4) enhanced the hypomotility induced by alpha-MT, (5) reduced the locomotor stimulation produced by levodopa plus benserazide, and (6) reduced central HVA, VMA, and 5-HIAA, but had no significant effects on central DA, NA, and 5-HT. These facts implied that Suanzaorentang decreased the turnover rate of central monoamines and central catecholaminergic activity. 相似文献
1000.
E Gluckman J Lotsberg A Devergie X M Zhao R Melo M Gomez-Morales M C Mazeron Y Pérol 《Revue fran?aise de transfusion et immuno-hématologie》1984,27(3):391-396
In a double-bind controlled study, oral Acyclovir has been compared to a placebo in a series of 39 consecutive patients undergoing bone marrow transplantation. A dose of 200 mg was given every 6 h from day 8 to day 35 after transplantation. Pharmacokinetic studies have shown the good absorption of the drug despite intestinal damage related to chemoradiotherapy or gut graft-versus-host disease (GVHD), there was no sign of toxicity. The protection against herpes simplex virus (HSV) infection was complete in the treated group when compared to the control group even in patients with high anti-HSV antibody titres. The same protection was observed against cytomegalovirus (CMV) infection. The incidence of HSV and CMV was the same in both groups after treatment ended. This study confirms the efficacy of Acyclovir against HSV infection and possibly against CMV infection when it is given prophylactically after bone marrow transplantation. 相似文献