全文获取类型
收费全文 | 1867篇 |
免费 | 129篇 |
出版年
2023年 | 3篇 |
2022年 | 19篇 |
2021年 | 30篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 30篇 |
2017年 | 12篇 |
2016年 | 51篇 |
2015年 | 99篇 |
2014年 | 95篇 |
2013年 | 112篇 |
2012年 | 154篇 |
2011年 | 159篇 |
2010年 | 102篇 |
2009年 | 84篇 |
2008年 | 85篇 |
2007年 | 103篇 |
2006年 | 79篇 |
2005年 | 86篇 |
2004年 | 108篇 |
2003年 | 78篇 |
2002年 | 83篇 |
2001年 | 49篇 |
2000年 | 44篇 |
1999年 | 41篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1996条查询结果,搜索用时 46 毫秒
101.
Biros E Kalina I Kohút A Bogyiová E Salagovic J Sulla I 《Physiological research / Academia Scientiarum Bohemoslovaca》2002,51(1):59-64
The polymorphisms of the tumor suppressor gene p53 in exon 4 (p53 BstUI) and in intron 6 (p53 MspI) have been suggested to be associated with the genetically determined susceptibility in diverse types of human cancer. In our hospital-based case-control study, we examined the allele and genotype incidence of these polymorphisms as well as their haplotype combinations in 60 brain tumor patients (27 males and 33 females) and 183 controls without malignancies. The genotype characteristics were determined by the PCR-based RFLP method using DNA extracted from peripheral blood. In this study we show that the p53 BstUI and the p53 MspI polymorphisms are not associated with increased risk of brain tumors. Thus, we conclude that the p53 BstUI and the p53 MspI polymorphic sites within the tumor suppressor gene p53 do not represent genetic determinants of susceptibility to brain tumors. 相似文献
102.
Yamamoto K Shibata F Miyasaka N Miura O 《Biochemical and biophysical research communications》2002,297(5):1245-1252
IL-12 activates STAT4 by inducing tyrosine phosphorylation, homo-dimerization, and nuclear translocation in NK cells and thereby stimulates proliferation and activation of these cells. The pore-forming protein perforin is a key effector protein for NK cell- and cytotoxic T lymphocyte-mediated cytolysis. Here we demonstrate that IL-12 induces the expression of the perforin gene in human NK cell line, NKL. Electrophoretic mobility shift assays using a probe containing two putative STAT-binding sequences located at -1085 and -1059 in the human perforin gene showed that STAT4 or STAT5 activated by IL-12 or IL-2, respectively, in NKL cells binds this region. Further analyses using various probes with or without mutated STAT-binding sequences showed that, although either of the two tandem STAT-binding sequences binds STAT4 weakly, the presence of both is required for significant binding of activated STAT4 and for formation of the STAT4-DNA-binding complex with lower electrophoretic mobility. Furthermore, mutation of either of the tandem STAT-binding sequences abolished the IL-12-induced activation of the perforin gene promoter in reporter gene assays. These results indicate that the IL-12-induced expression of the perforin gene in NK cells is directly regulated by STAT4, which binds, most likely as a homo-tetramer, to the tandem STAT-binding sequences in the perforin gene promoter. 相似文献
103.
Goh YL Yasin R Puthucheary SD Koh YT Lim VK Taib Z Thong KL 《Journal of applied microbiology》2003,95(5):1134-1142
AIMS: DNA fingerprinting of Salmonella enterica serotype Paratyphi B isolated in Malaysia during 1982-83, 1992 and 1996-2002 was carried out by pulsed-field gel electrophoresis (PFGE), antimicrobial susceptibility tests and D-tartrate utilization tests to assess the extent of genetic diversity of these isolates in Malaysia. METHODS AND RESULTS: Eighty-six human isolates and one food isolate of Salm. Paratyphi B were analysed by PFGE, antimicrobial susceptibility tests and D-tartrate utilization tests. Sixty-five strains were D-tartrate-negative (dT-) while 22 strains were D-tartrate-positive (dT+). Thirty-seven per cent of the Salm. Paratyphi B strains were resistant to one or more antimicrobial agents. PFGE analysis clearly distinguished the dT- and dT+ strains into two clusters based on the unweighted pair group average method (UPGMA). Twenty-two XbaI-pulsotypes were observed among the 65 dT- strains while 17 XbaI-pulsotypes were observed among the 22 isolates of Salm. Paratyphi B dT+. CONCLUSIONS: The present study showed that PFGE was very discriminative with 33.7% of the strains yielding distinct fingerprints. Paratyphoid fever in Malaysia is probably caused by one predominant, endemic clone of Salm. Paratyphi B dT- with various subtypes. There was no association between the pulsotypes and the severity of the disease indicating that the severity of the disease is probably multifactorial. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings of the present study verify the usefulness of PFGE in characterizing strains of Salm. Paratyphi B. This is the first report on the application of PFGE on a large collection of Salm. Paratyphi B in Malaysia. 相似文献
104.
Hot-water extract from mycelia of Cordyceps sinensis as a substitute for antibiotic growth promoters 总被引:2,自引:0,他引:2
Broiler chicks were orally dosed with a hot-water extract of mycelia from Cordyceps sinensis (CS-HW) to assess possible substitution of Avilamycin as an antibiotic growth promoter (AGP). The growth performance (body weight gain and survivability) and the health index (the microflora in the small intestines and the antibody titer to Newcastle disease virus) of chicks were significantly improved in the CS-HW (600 mg/kg diet) and the Avilamycin (20 mg/kg diet) fed group in comparison with the control group (p<0.05). The Avilamycin-fed group and the CS-HW-fed group had similar growth performances but the latter gave a better microbial flora in the small intestines. These results indicate that CS-HW enhances the physiological activity in chicks and can be used as a substitute for AGPs. 相似文献
105.
The ion-exchange chromatography behavior of recombinant glucose dehydrogenase harboring pyrroloquinoline quinone (PQQGDH) was modified to greatly simplify its purification. The surface charge of PQQGDH was engineered by either fusing a three-arginine tail to the C-terminus of PQQGDH (PQQGDH+Arg3) or by substituting three residues exposed on the surface of the enzyme to Arg by site-directed mutagenesis (3RPQQGDH). During cation exchange chromatography, both surface charge-engineered enzymes eluted at much higher salt concentrations than the wild-type enzyme. After the chromatography purification step, both PQQGDH+Arg3 and 3RPQQGDH appeared as single bands on SDS-PAGE, while extra bands appeared with the wild-type protein sample. Although all tested kinetic parameters of both engineered enzymes are similar to those of wild type, both modifications resulted in enzymes with increased thermal stability. Our achievements have resulted in the greater production of an improved quality PQQGDH by a simplified process. 相似文献
106.
107.
Verstreken P Koh TW Schulze KL Zhai RG Hiesinger PR Zhou Y Mehta SQ Cao Y Roos J Bellen HJ 《Neuron》2003,40(4):733-748
We describe the isolation and characterization of Drosophila synaptojanin (synj) mutants. synj encodes a phosphatidylinositol phosphatase involved in clathrin-mediated endocytosis. We show that Synj is specifically localized to presynaptic terminals and is associated with synaptic vesicles. The electrophysiological and ultrastructural defects observed in synj mutants are strikingly similar to those found in endophilin mutants, and Synj and Endo colocalize and interact biochemically. Moreover, synj; endo double mutant synaptic terminals exhibit properties that are very similar to terminals of each single mutant, and overexpression of Endophilin can partially rescue the functional defects in partial loss-of-function synj mutants. Interestingly, Synj is mislocalized and destabilized at synapses devoid of Endophilin, suggesting that Endophilin recruits and stabilizes Synj on newly formed vesicles to promote vesicle uncoating. Our data also provide further evidence that kiss-and-run is able to maintain neurotransmitter release when synapses are not extensively challenged. 相似文献
108.
Cho SJ Cho PY Lee MS Hur SY Lee JA Kim SK Koh KS Na YE Choo JK Kim CB Park SC 《Development genes and evolution》2003,213(4):207-210
The Hox genes of the oligochaete, Perionyx excavatus, were surveyed using PCR and phylogenetic analysis. We were able to identify 11 different Hox gene fragments. Comparative and phylogenetic analyses revealed that this oligochaete would have at least five Hox genes of the anterior group, including three copies of labial-type, five of the central group and one of the posterior group. This is the first report regarding sequence information and phylogenetic analysis of Hox genes in the earthworm. 相似文献
109.
Erickson RH Yoon BC Koh DY Kim DH Kim YS 《American journal of physiology. Gastrointestinal and liver physiology》2001,281(5):G1221-G1227
Induction of angiotensin-converting enzyme was examined in proximal and distal intestinal segments of rats fed a low-protein (4%) diet and then switched to a high-protein (gelatin) diet. Animals were killed at varying time points, and brush-border membranes and total RNA were prepared from the segments. In the proximal intestine, there was a fivefold increase in angiotensin-converting enzyme levels after 14 days but only a twofold change in mRNA. In the distal intestine, there was no increase in enzyme activity but mRNA increased 2.4-fold. Organ culture was used to measure changes in enzyme biosynthesis. There was a 5- to 6-fold increase in the biosynthesis of angiotensin-converting enzyme in the proximal intestine 24 h after the switch to the gelatin diet and a 1.6-fold increase in mRNA levels. No change in biosynthesis was observed in the distal small intestine despite an increase in mRNA. These results support the conclusion that rapid dietary induction of intestinal angiotensin-converting enzyme is differentially regulated in proximal and distal segments of the small intestine. 相似文献
110.