全文获取类型
收费全文 | 701629篇 |
免费 | 67080篇 |
国内免费 | 456篇 |
出版年
2018年 | 7732篇 |
2017年 | 7244篇 |
2016年 | 9890篇 |
2015年 | 12514篇 |
2014年 | 14592篇 |
2013年 | 20928篇 |
2012年 | 22965篇 |
2011年 | 23352篇 |
2010年 | 15927篇 |
2009年 | 14247篇 |
2008年 | 20318篇 |
2007年 | 20928篇 |
2006年 | 19858篇 |
2005年 | 18543篇 |
2004年 | 18484篇 |
2003年 | 17736篇 |
2002年 | 17324篇 |
2001年 | 28598篇 |
2000年 | 28606篇 |
1999年 | 22673篇 |
1998年 | 7990篇 |
1997年 | 8103篇 |
1996年 | 7814篇 |
1995年 | 7309篇 |
1994年 | 7170篇 |
1993年 | 7000篇 |
1992年 | 18838篇 |
1991年 | 18423篇 |
1990年 | 18427篇 |
1989年 | 18063篇 |
1988年 | 16850篇 |
1987年 | 16042篇 |
1986年 | 14731篇 |
1985年 | 15391篇 |
1984年 | 12571篇 |
1983年 | 10869篇 |
1982年 | 8250篇 |
1981年 | 7432篇 |
1980年 | 6944篇 |
1979年 | 12046篇 |
1978年 | 9309篇 |
1977年 | 8794篇 |
1976年 | 8386篇 |
1975年 | 9380篇 |
1974年 | 10161篇 |
1973年 | 10014篇 |
1972年 | 9110篇 |
1971年 | 8351篇 |
1970年 | 7415篇 |
1969年 | 7250篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
L. N. GILLMAN D. J. KEELING R. C. GARDNER S. D. WRIGHT 《Journal of evolutionary biology》2010,23(6):1327-1330
A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome. 相似文献
22.
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
23.
Airway area by acoustic reflections measured at the mouth 总被引:5,自引:0,他引:5
Fredberg J. J.; Wohl M. E.; Glass G. M.; Dorkin H. L. 《Journal of applied physiology》1980,48(5):749-758
24.
P C de Visser N M A J Kriek P A V van Hooft A Van Schepdael D V Filippov G A van der Marel H S Overkleeft J H van Boom D Noort 《The journal of peptide research》2003,61(6):298-306
As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity. 相似文献
25.
R N Korotkina A A Papin A A Karelin 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(10):438-440
Experiments on 330 rats were made to study the influence of benzodiazepines (diazepam, dormicum and phenazepam) on 5'-nucleotidase activity in brain homogenates. It was discovered that diazepam and dormicum in doses of 3 and 4 mg, phenazepam in doses of 3.75 and 5 mg per 200 g bw provoked a 16-20% reduction in 5'-nucleotidase activity. The maximal effect of diazepam (3 and 4 mg doses) was attained 1 h after intraperitoneal injection, that of dormicum (3 mg) 30 min and of phenazepam (5 mg) 1 h after intraperitoneal injection. It is assumed that benzodiazepines are involved in AMP metabolism. 相似文献
26.
R. A. Mueller M. J. Rosner J. N. Ghia S. K. Powers E. R. Kafer R. D. Hunt 《Cellular and molecular neurobiology》1988,8(2):235-243
1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury. 相似文献
27.
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
28.
29.
30.
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