全文获取类型
收费全文 | 473955篇 |
免费 | 49303篇 |
国内免费 | 185篇 |
专业分类
523443篇 |
出版年
2018年 | 4301篇 |
2016年 | 5657篇 |
2015年 | 6906篇 |
2014年 | 8518篇 |
2013年 | 12277篇 |
2012年 | 13667篇 |
2011年 | 14276篇 |
2010年 | 9771篇 |
2009年 | 8796篇 |
2008年 | 12672篇 |
2007年 | 13369篇 |
2006年 | 12514篇 |
2005年 | 11974篇 |
2004年 | 12163篇 |
2003年 | 11843篇 |
2002年 | 11693篇 |
2001年 | 21106篇 |
2000年 | 21380篇 |
1999年 | 16682篇 |
1998年 | 5698篇 |
1997年 | 5862篇 |
1996年 | 5451篇 |
1995年 | 5238篇 |
1994年 | 5131篇 |
1993年 | 5128篇 |
1992年 | 14182篇 |
1991年 | 13860篇 |
1990年 | 13503篇 |
1989年 | 13189篇 |
1988年 | 12346篇 |
1987年 | 11839篇 |
1986年 | 10688篇 |
1985年 | 10894篇 |
1984年 | 8956篇 |
1983年 | 7816篇 |
1982年 | 5853篇 |
1981年 | 5171篇 |
1980年 | 5001篇 |
1979年 | 8839篇 |
1978年 | 6796篇 |
1977年 | 6248篇 |
1976年 | 5759篇 |
1975年 | 6492篇 |
1974年 | 7187篇 |
1973年 | 7173篇 |
1972年 | 6637篇 |
1971年 | 6158篇 |
1970年 | 5296篇 |
1969年 | 5097篇 |
1968年 | 4655篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Y Tani I Ohkubo S Higashiyama M Kunimatsu M Sasaki 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,88(2):429-441
1. High mol. wt kininogen (HMW kininogen) was purified to a homogeneous state from porcine plasma. 2. The protein exhibited a strong inhibitory activity for thiol proteinases such as ficin, papain and calpain I, whereas it did not inhibit serine proteinases, trypsin and chymotrypsin. 3. The mol. wt, isoelectric point, amino acid and carbohydrate compositions, stabilities to temperature and pH, kinetic constants, and immunological properties of the porcine HMW kininogen were determined and compared with those of human HMW kininogen. 相似文献
12.
B B Fuks N F Avrova L V Van'ko N A Starosvetskaia M N Boltovskaia 《Biulleten' eksperimental'no? biologii i meditsiny》1986,101(1):66-68
Female BALB/c mice were immunized with human melanoma (Mewo) cells containing ganglioside GD3 as a surface antigen. Immune splenocytes were fused with syngeneic P3-X63.Ag 8 myeloma cells. Antibodies produced by hybrid clones were analyzed by solid phase immunoassay. B, C, D and Q clones producing antibodies against Raja clavata brain gangliosides were obtained. Monoclonal B and C antibodies bound monosialogangliosides. Monoclonal D antibody bound a number of gangliosides but reacted predominantly with GD1a. Monoclonal Q antibody reacted selectively with GQ1c. It is assumed that ganglioside GQ1c is expressed on the melanoma cell surface and may be found only in the early stage of ontogenesis of high vertebrates. 相似文献
13.
The degree of serotiny (i.e. the proportion of follicles remaining closed in each year's crop of cones since the last fire) was measured in Bank-sia attenuata, B. menziesii and B. prionotes at five sites along a climatic gradient extending 500 km north of Perth, Western Australia. The decrease in annual rainfall and increase in average temperature along the gradient paralleled a decrease in plant height and an increase in the degree of serotiny of all species. Extreme serotiny was recorded in the scrub-heath at the xeric end of the gradient whereas two species were essentially non-serotinous in the low woodland at the most mesic site. It is concluded that degree of serotiny is related to the fire characteristics of the site which depend on plant height. In xeric scrub-heath, the entire canopies of the Banksia spp. are consumed by fire which promotes massive release of seed. This facilitates recruitment in an otherwise unpredictable and unreliable seedbed. In mesic woodland, where cones rarely come into contact With flames, seeds are released spontaneously and site conditions are more conducive to recruitment in the inter-fire period. 相似文献
14.
15.
16.
Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues. 相似文献
17.
The immunological analysis of 24 spontaneous Strr, Rifr and Kanr mutants of streptococcal strain IP, highly virulent for mice and capable of binding polyclonal human IgG (IgG FcR+), was made. The characteristic feature of all these mutants was decreased virulence, restored after their passage in vivo. 23 mutants were capable of binding polyclonal IgG; one Strr mutant had no such capacity, but acquired it, together with an increase in virulence, after its passage in vivo. When stored in meat-peptone agar without antibiotics, 5 out of 10 Strr mutants lost their capacity for binding polyclonal human IgG. After passage in vivo they regained this property simultaneously with virulence. 相似文献
18.
K I Savitskaia A A Vorob'ev G G Sinitsina 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(12):24-31
The results of the inoculation of material taken from the anterior section of the nasal cavity and from the pharyngeal mucosa of 50 healthy young children and 298 acute pneumonia patients were analyzed. 23 microbial species were isolated. In the samples taken from the anterior section of the nasal cavity, monocultures were detected in 86 samples and 54 variants of associations including 2-4 species, in 139 samples. In the samples taken from the pharynx, monocultures were detected in 59 samples and 180 variants of associations including 2-6 species, in 282 samples. Differences in the contamination of the nasal cavity and the pharynx in healthy children and in pneumonia patients were revealed. These differences were manifested in the structure of the microflora (monocultures, associations, their composition), the assortment of microbial species and their concentration. In young children with pneumonia the microflora of the upper respiratory tract was found to reflect the severity of acute pneumonia and the intensity of the pathological process in the lungs (uncomplicated, pyodestructive pneumonia, pyodestructive pneumonia with fatal termination, acute purulent pleurisy). 相似文献
19.
M S Bortnik A V Skurat I R Eshba T V Bulargina E S Severin 《Biokhimii?a (Moscow, Russia)》1985,50(4):589-594
Changes in the properties of adenylate cyclase from the lungs of tuberculotic guinea pigs were revealed. The number of beta-adrenergic receptors in the lungs was found to be reduced by 30% at the second and by 70% at the third stage of the disease. The degree and the value of Ka for adenylate cyclase activation by isoproterenol remained thereby unchanged. The basal activity of adenylate cyclase was increased by 20% against the control level at the second stage and decreased by 20% at the third stage of the disease. At these periods, the stimulating effects of guanylyl imidodiphosphate, NaF and forskolin on lung adenylate cyclase were diminished. The experimental results point to the significant role of the enzymes of cAMP metabolism and reflect the course of the tuberculosis process in experimental animals. 相似文献
20.
Immunological characterization of the cytochrome o terminal oxidase from Escherichia coli 总被引:13,自引:0,他引:13
The cytochrome o terminal oxidase from Escherichia coli was immunochemically purified and monospecific antiserum toward cytochrome o was obtained. This antiserum is able to precipitate 100% of the ubiquinol-1 oxidase activity in Triton X-100 extracts of membranes from an E. coli strain in which cytochrome o is the only terminal oxidase. Cytochrome o was analyzed and quantitated using crossed immunoelectrophoresis, rocket immunoelectrophoresis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that cytochrome o is composed of four subunits of approximate equimolar stoichiometry with molecular weights of 51,000, 28,500, 18,000, and 12,700. The low temperature (77 K) reduced - oxidized spectrum of the immunoprecipitate shows two peaks at 555 and 562 nm, indicating b-type cytochromes. With the anti-cytochrome o and antiserum toward the cytochrome d terminal oxidase complex which was previously obtained, it is possible to immunochemically assay for all the cytochromes in the cytoplasmic membrane of aerobically grown E. coli. Preliminary results indicate that the biosynthesis of cytochrome o is repressed when cytochrome d is induced by lowering the dissolved oxygen concentration during cell growth. 相似文献