全文获取类型
收费全文 | 9299篇 |
免费 | 531篇 |
国内免费 | 5篇 |
出版年
2022年 | 30篇 |
2021年 | 91篇 |
2020年 | 72篇 |
2019年 | 64篇 |
2018年 | 117篇 |
2017年 | 84篇 |
2016年 | 185篇 |
2015年 | 282篇 |
2014年 | 302篇 |
2013年 | 612篇 |
2012年 | 554篇 |
2011年 | 605篇 |
2010年 | 356篇 |
2009年 | 311篇 |
2008年 | 564篇 |
2007年 | 593篇 |
2006年 | 553篇 |
2005年 | 544篇 |
2004年 | 594篇 |
2003年 | 493篇 |
2002年 | 492篇 |
2001年 | 181篇 |
2000年 | 151篇 |
1999年 | 147篇 |
1998年 | 128篇 |
1997年 | 98篇 |
1996年 | 99篇 |
1995年 | 90篇 |
1994年 | 84篇 |
1993年 | 76篇 |
1992年 | 92篇 |
1991年 | 104篇 |
1990年 | 94篇 |
1989年 | 96篇 |
1988年 | 91篇 |
1987年 | 75篇 |
1986年 | 71篇 |
1985年 | 57篇 |
1984年 | 50篇 |
1983年 | 57篇 |
1982年 | 48篇 |
1981年 | 47篇 |
1980年 | 44篇 |
1979年 | 46篇 |
1978年 | 24篇 |
1977年 | 46篇 |
1974年 | 24篇 |
1973年 | 28篇 |
1971年 | 26篇 |
1970年 | 25篇 |
排序方式: 共有9835条查询结果,搜索用时 15 毫秒
31.
32.
Summary The antimetastatic effect of Lactobacillus casei YIT9018 (LC 9018) against Lewis lung carcinoma (3LL) in C57BL/6 mice was determined. Intrapleural (i.pl.) administration of LC 9018 was effective in inhibiting pulmonary metastasis after s.c. inoculation of 3LL tumors into C57BL/6 mice. The combination of i.pl. and intralesional or i.v. injections of LC 9018 also markedly inhibited pulmonary metastasis in 3LL-bearing mice. The i.pl. administration of LC 9018 into mice induced an increase in the number of thoracic exudate cells (TEC) and the cell population in the TEC was mainly polymorphonuclear leukocytes in the early stage, while macrophages were dominant in the late stage. In addition, in vitro cytolytic activity against 3LL cells and natural killer cell activity of TEC were augmented by the i.pl. administration of LC 9018. Furthermore, i.pl. administration of LC 9018 into the mice rendered their lung macrophages tumoricidal for 3LL cells in vitro. These results show that TEC induced by i.pl. administration of LC 9018 played a key role in the inhibtion of metastasis in 3LL-bearing mice. 相似文献
33.
Hydrogen Peroxide-dependent Synthesis of Flavonols in Mesophyll Cells of Vicia faba L. 总被引:2,自引:0,他引:2
Mesophyll cells of Vicia faba contain kaempferol and quercetinglycosides. When isolated mesophyll cells were treated with0.1 mM H2O2 for 2 h, the levels of these flavonols increasedby 1070% of the control values (mean values, 19.6% and34.4% for kaempferol and quercetin glycosides, respectively).Such increases in levels of flavonols were also observed inisolated vacuoles of mesophyll cells. However, when mesophyllcells and vacuoles were treated with 10 mM H2O2)degradationof flavonols was observed. These data suggest that H2O2 hastwo effects on the metabolism of flavonols: induction of theirsynthesis and stimulation of their oxidation. (Received March 6, 1989; Accepted July 10, 1989) 相似文献
34.
Takeshi Tsunetoshi Atsuhiro Otsuka Hiroshi Mikami Katsuhiko Kohara Katsutoshi Katahira Toshio Ogihara 《European journal of applied physiology and occupational physiology》1989,58(7):705-709
We have previously demonstrated that blood pressure elevation by acute blood volume expansion is volume-dependent during the infusion period and resistance-dependent in the post-infusion period in normal anesthetized dogs, and that such an increase in blood pressure is associated with a potentiation of the pressor response to norepinephrine. To evaluate the possible renal contribution to these hemodynamic changes, blood volume expansion was performed for 1 h with dextran dissolved in lactated Ringer's solution (20 ml/kg) in 15 nephrectomized dogs. The mean blood pressure, cardiac output and total peripheral resistance at the end of infusion were 126%, 225% and 60%, respectively; 3 h after volume expansion they were 126%, 151%, and 92% respectively. However, in 4 dogs, there was an increase in mean blood pressure (138%) 3 h after volume expansion. This was thought to result from an increase in the total peripheral resistance (133%) associated with the recovery of cardiac output (106%). The pressor response to norepinephrine (0.5 microgram/kg) was potentiated after volume expansion. These results indicate that the handling of volume by the kidney contributed to the maintenance of an elevated level of cardiac output. However, nephrectomy did not seem to interfere with the hemodynamic switching of the causative factor for blood pressure elevation from increased cardiac output to increased total peripheral resistance. Neither was the potentiation of pressor response to norepinephrine affected. 相似文献
35.
Osamu Kondo Hiroyuki Honda Masahito Taya Takeshi Kobayashi 《Applied microbiology and biotechnology》1989,32(3):291-294
Summary Growth properties of carrot hairy root cells in various bioreactors were investigated. A turbine-blade reactor and an immobilized rotating drum reactor were found to be advantageous for the hairy root culture because of a high oxygen transfer coefficient (k in L a). After 30 days of culture, 10 g/l of dry hairy root cells were obtained in both bioreactors and maximum growth rates (V
m
) were found to be 0.63 and 0.61 g/l per day for the turbine-blade reactor and immobilized rotating drum reactor, respectively. Specific growth rates () at various cultivation times were observed to be linearly proportional to X/k
l
a for both bioreactor configurations where X is the cell concentration. The estimated specific oxygen uptake rate of 0.34 mmol O2/g dry cells per hour compares fairly well with an experimental value of 0.3. 相似文献
36.
T Maruyama T Nomiyama M Asahi N Mori E Ono A Kawahara S Fujimoto 《Histology and histopathology》1989,4(1):85-94
Based on ultrastructural features of cellular components of a hemangiopericytoma, hyperplastic cells are classifiable into fibroblast-like (group I), endotheloid (group II) and pericyte-like (group III) cells. The transformation of the group I cells to the group II, or to the group III cells, is pronounced in our electron micrographs and this may imply that the group I cell is the principal cell of origin in this neoplasm. The smooth muscle-like (group IV) cells comprising the media of the arteries and veins in this neoplasm may represent modified, possibly de-differentiated smooth muscle cells reacted to the neoplastic proliferation of the surrounding adventitial (group I) cells. 相似文献
37.
38.
Induction of manganese superoxide dismutase by tumor necrosis factor in human breast cancer MCF-7 cell line and its TNF-resistant variant 总被引:3,自引:0,他引:3
K Asoh Y Watanabe H Mizoguchi M Mawatari M Ono K Kohno M Kuwano 《Biochemical and biophysical research communications》1989,162(2):794-801
Tumor necrosis factor (TNF)-resistant variant of human mammary cancer MCF-7 cell line was isolated by stepwise selection. The final TNF-resistant variant Tnf-1000 showed more than 100-fold higher resistance than the parental MCF-7 cell. Saturation kinetics for 125I-TNF binding showed that TNF-1000 cells had similar TNF receptor numbers as MCF-7 cells, but of a lower affinity. Induction of superoxide dismutase (SOD) was compared between MCF-7 and Tnf-1000 cells treated with TNF: SOD scavenges potentially toxic superoxide radicals. TNF induced more mitochondrial manganese SOD (SODm) in MCF-7 than in Tnf-1000 whereas there appeared to be no significant induction of cytosolic copper/zinc SOD (SODc) by TNF in both MCF-7 and Tnf-1000 cell lines. Acquirement of TNF-resistance in MCF-7 cells might be correlated with expression of SODm. 相似文献
39.
Mitochondrial DNA polymorphism in native Philippine cattle based on restriction endonuclease cleavage patterns 总被引:4,自引:0,他引:4
Tomomasa Watanabe Joseph S. Masangkay Shigeharu Wakana Naruya Saitou Takeshi Tomita 《Biochemical genetics》1989,27(7-8):431-438
An analysis of patterns of cleavage of mtDNA by restriction endonucleases was performed for nine individuals from the Philippine
population of native cattle. MtDNA polymorphisms were detected in the restriction patterns generated by the following six
enzymes,BamHI,BglII,EcoRV,HindIII,PstI, andScaI. The restriction patterns showing polymorphisms were distributed nonrandomly among the nine individuals examined from the
Philippine population of native cattle, indicating the existence of two separate types of mtDNA. These two types of mtDNA
are very different from each other, at the level of subspecies. Since the native Philippine cattle are considered to represent
an admixture of European and Indian cattle, the two types of mtDNA must be derived from the mtDNAs of both varieties. The
polymorphic sites in mtDNA have been located on a restriction map, and the nucleotide substitutions at some of the sites have
also been estimated. 相似文献
40.
Riichi Tawa Tetsuya Ono Akihiro Kurishita Shigefumi Okada Shingo Hirose 《Differentiation; research in biological diversity》1990,45(1):44-48
DNA methylation in an adult mammalian body shows tissue-specificity. But when and how the specificity is established in the process of development has not yet been elucidated. Here we have investigated age-dependent changes in the amount of 5-methyldeoxycytidine (5mdC) that DNA of various mouse tissues contains during the late-fetal and postnatal periods, using high-performance liquid chromatography. The tissue-specificity in the 5mdC level was observed in the late-fetal stage, and the level continued to change during the subsequent periods. The most pronounced alterations were observed in brain and liver, where similar biphasic changes were seen, but at different ages. At maturation, the 5mdC levels were high in thymus, spleen and brain, intermediate in lung, and low in liver and sperm. The data demonstrate the importance of the peri- and postnatal periods in establishment of tissue-specificity in 5mdC content. 相似文献