全文获取类型
收费全文 | 1027590篇 |
免费 | 107345篇 |
国内免费 | 410篇 |
出版年
2018年 | 9739篇 |
2017年 | 9236篇 |
2016年 | 13191篇 |
2015年 | 17108篇 |
2014年 | 20301篇 |
2013年 | 29244篇 |
2012年 | 32848篇 |
2011年 | 33558篇 |
2010年 | 22905篇 |
2009年 | 21147篇 |
2008年 | 29984篇 |
2007年 | 31266篇 |
2006年 | 29241篇 |
2005年 | 28081篇 |
2004年 | 27610篇 |
2003年 | 26740篇 |
2002年 | 26223篇 |
2001年 | 45863篇 |
2000年 | 45675篇 |
1999年 | 36439篇 |
1998年 | 13095篇 |
1997年 | 13293篇 |
1996年 | 12709篇 |
1995年 | 11736篇 |
1994年 | 11433篇 |
1993年 | 11321篇 |
1992年 | 30033篇 |
1991年 | 29357篇 |
1990年 | 28592篇 |
1989年 | 27750篇 |
1988年 | 25605篇 |
1987年 | 24318篇 |
1986年 | 22669篇 |
1985年 | 22522篇 |
1984年 | 18574篇 |
1983年 | 16166篇 |
1982年 | 12262篇 |
1981年 | 11090篇 |
1980年 | 10302篇 |
1979年 | 17498篇 |
1978年 | 13656篇 |
1977年 | 12316篇 |
1976年 | 11648篇 |
1975年 | 13103篇 |
1974年 | 13967篇 |
1973年 | 13734篇 |
1972年 | 12611篇 |
1971年 | 11128篇 |
1970年 | 9817篇 |
1969年 | 9574篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
911.
912.
L Chrobák D Radochová K Smetana F Mat?ja M Kout J Polák P Dít? J Pribrosky I Dvorácková 《Folia haematologica (Leipzig, Germany : 1928)》1980,107(4):628-640
These siblings of a Czech family aged 21, 19 and 6 years, respectively, with congenital dyserythropoietic anemia, type II, (HEMPAS) are reported. In two elder siblings ferrokinetic studies revealed a rapid plasma 59Fe clearance, markedly decreased erythrocyte incorporation and shortened 51Cr red-cell survival. Direct anti-globulin test was found positive in one of them. Further investigations revealed low values of blood plasma cholesterol, total lipids, beta-lipoproteins, beta-carotine and vitamin E and A as well as low values of the prothrombin complex. Liver biopsy demonstrated siderosis and disseminated intravascular coagulation in the liver in both patients. The possible reasons for these humoral aberrations are discussed. 相似文献
913.
914.
The interpretation of a moving retinal image 总被引:10,自引:0,他引:10
H C Longuet-Higgins K Prazdny 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1980,208(1173):385-397
It is shown that from a monocular view of a rigid, textured, curved surface it is possible, in principle, to determine the gradient of the surface at any point, and the motion of the eye relative to it, from the velocity field of the changing retinal image, and its first and second spatial derivatives. The relevant equations are redundant, thus providing a test of the rigidity assumption. They involve, among other observable quantities, the components of shear of the retinal velocity field, suggesting that the visual system may possess specialized channels for computing these components. 相似文献
915.
C Toga-Piquet A S Henderson J M Grillo A M Vagner-Capodano A Stahl 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1984,298(14):383-386
The Pig chromosomes that contain rDNA sites displayed a polymorphism in the distribution of the genes among the nucleolar organizers located on pairs Nos. 8 and 10. Two, or more often three, active sites were observed in the chromosomes of lymphocytes stimulated with phytohemagglutinin. Only 5% of the metaphases showed a 4th small active site. At the onset of stimulation most cells contained one-two nucleoli; four nucleoli were never observed. After prolonged stimulation, the number of nuclei containing three nucleoli increased. A 4th small nucleolus appeared in a few cells, presumably formed by activation of the smallest rDNA site. 相似文献
916.
M A Chamberlain 《BMJ (Clinical research ed.)》1985,290(6480):1449-1450
917.
918.
Analogs of the molluscan neuropeptide FMRFamide were tested on four different molluscan muscle preparations which show qualitatively different responses to the peptide; the structure-activity relations are basically similar, but not identical. The C-terminal amide and the Arg3 residue are critical for FMRFamide-like activity on all four preparations. In contrast, analogs extended at the N-terminal or with conservative substitutions for the Phe1 or Met2 residue are approximately equipotent to FMRFamide. These structural requirements parallel those for the C-terminal tetrapeptide amide of gastrin. 相似文献
919.
Genomic technologies are revealing several mechanisms of insecticide resistance involving enhanced detoxification or reduced target-site sensitivity that had previously defied molecular analyses. Genome projects are also revealing some potentially far-reaching consequences for pest-insect genomes of the rapid accumulation of multiple resistance mutations in very short periods of evolutionary time. 相似文献
920.
J T Brosnan M E Brosnan M Yudkoff I Nissim Y Daikhin A Lazarow O Horyn I Nissim 《The Journal of biological chemistry》2001,276(34):31876-31882
We have utilized [(15)N]alanine or (15)NH(3) as metabolic tracers in order to identify sources of nitrogen for hepatic ureagenesis in a liver perfusion system. Studies were done in the presence and absence of physiologic concentrations of portal venous ammonia in order to test the hypothesis that, when the NH(4)(+):aspartate ratio is >1, increased hepatic proteolysis provides cytoplasmic aspartate in order to support ureagenesis. When 1 mm [(15)N]alanine was the sole nitrogen source, the amino group was incorporated into both nitrogens of urea and both nitrogens of glutamine. However, when studies were done with 1 mm alanine and 0.3 mm NH(4)Cl, alanine failed to provide aspartate at a rate that would have detoxified all administered ammonia. Under these circumstances, the presence of ammonia at a physiologic concentration stimulated hepatic proteolysis. In perfusions with alanine alone, approximately 400 nmol of nitrogen/min/g liver was needed to satisfy the balance between nitrogen intake and nitrogen output. When the model included alanine and NH(4)Cl, 1000 nmol of nitrogen/min/g liver were formed from an intra-hepatic source, presumably proteolysis. In this manner, the internal pool provided the cytoplasmic aspartate that allowed the liver to dispose of mitochondrial carbamyl phosphate that was rapidly produced from external ammonia. This information may be relevant to those clinical situations (renal failure, cirrhosis, starvation, low protein diet, and malignancy) when portal venous NH(4)(+) greatly exceeds the concentration of aspartate. Under these circumstances, the liver must summon internal pools of protein in order to accommodate the ammonia burden. 相似文献