全文获取类型
收费全文 | 15350篇 |
免费 | 1417篇 |
国内免费 | 6篇 |
专业分类
16773篇 |
出版年
2023年 | 41篇 |
2022年 | 91篇 |
2021年 | 171篇 |
2020年 | 126篇 |
2019年 | 134篇 |
2018年 | 172篇 |
2017年 | 179篇 |
2016年 | 349篇 |
2015年 | 570篇 |
2014年 | 646篇 |
2013年 | 762篇 |
2012年 | 1094篇 |
2011年 | 1166篇 |
2010年 | 767篇 |
2009年 | 692篇 |
2008年 | 920篇 |
2007年 | 1024篇 |
2006年 | 868篇 |
2005年 | 882篇 |
2004年 | 921篇 |
2003年 | 862篇 |
2002年 | 825篇 |
2001年 | 168篇 |
2000年 | 123篇 |
1999年 | 221篇 |
1998年 | 255篇 |
1997年 | 165篇 |
1996年 | 167篇 |
1995年 | 156篇 |
1994年 | 158篇 |
1993年 | 150篇 |
1992年 | 140篇 |
1991年 | 98篇 |
1990年 | 114篇 |
1989年 | 101篇 |
1988年 | 111篇 |
1987年 | 92篇 |
1986年 | 92篇 |
1985年 | 93篇 |
1984年 | 128篇 |
1983年 | 92篇 |
1982年 | 120篇 |
1981年 | 114篇 |
1980年 | 98篇 |
1979年 | 55篇 |
1978年 | 66篇 |
1977年 | 64篇 |
1976年 | 66篇 |
1975年 | 47篇 |
1974年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Dimitri S. Monos Eszter Czanky Santa J. Ono Susan F. Radka Dietmar Kappes Jack L. Strominger 《Immunogenetics》1995,42(3):172-180
cDNAs coding for the HLA class II DR and DQ and chains of the diabetogenic haplotypes DR3 and DR4 were introduced into a mammalian expression vector and transfected into L-cell mouse fibroblasts to produce cells expressing individual human class II molecules. Stable L transfectants were generated expressing each of the DR or DQ isotypes of the cis-encoded and chains of the DR3 or DR4 haplotypes, as well as the trans-encoded and chains of the DQ molecules of the two haplotypes. However, isotype mismatched combinations (DR/DQ or DQ/DR) did not result in any stable transfectants. The stable DQ L-cell transfectants obtained, along with homozygous B-cell lines expressing the DQ2 and DQ8 specificities, were tested against a large panel of twentyone anti-HLA class II monoclonal antibodies (mAbs). Their unusual reactivity patterns are described including the failure of most pan-DQ mAbs to react with all DQ expressing L-cell transfectants. Interestingly, some mAbs react with certain heterodimers expressed on B-LCL but fail to recognize the same heterodimers expressed on the transfectants. This is suggestive of minor structural modifications that class II molecules undergo depending on the cells they are expressed on.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number U07848. The name DQB1
*
0202 was officially assigned by the WHO Nomenclature Committee in April 1994. This follows the agreed policy that, subject to the conditions stated in the most recent Nomenclature Report (Bodmer et al. 1992), names will be assigned to new sequences as they are identified. Lists of such new names will be published in the following WHO Nomenclature Report 相似文献
192.
Donald R. Gehlert Douglas A. Schober Susan L. Gackenheimer 《Journal of neurochemistry》1995,64(6):2792-2800
Abstract: ( R )-[3 H]Tomoxetine is a radioligand that binds to the norepinephrine (NE) uptake site with high affinity but also binds to a second, lower-affinity site. The goal of the present study was to identify the nature of this low-affinity site by comparing the binding properties of ( R )-[3 H]tomoxetine with those of ( R/S )-[3 H]nisoxetine, a highly selective ligand for the NE uptake site. In homogenate binding studies, both radioligands bound to the NE uptake site with high affinity, whereas ( R )-[3 H]tomoxetine also bound to a second, lower-affinity site. The autoradiographic distribution of binding sites for both radioligands is consistent with the known distribution of NE-containing neurons. However, low levels of ( R )-[3 H]-tomoxetine binding were seen in the caudate-putamen, globus pallidus, olfactory tubercle, and zona reticulata of the substantia nigra, where ( R/S )-[3 H]nisoxetine binding was almost absent. In homogenates of the caudate-putamen, the NE uptake inhibitors desipramine and ( R )-nisoxetine and the serotonin (5-HT) uptake inhibitor citalopram produced biphasic displacement curves. Autoradiographic studies using 10 n M ( R )-nisoxetine to mask the binding of ( R )-[3 H]tomoxetine to the NE uptake site produced autoradiograms that were similar to those produced by [3 H]citalopram. Therefore, ( R )-[3 H]tomoxetine binds to the NE uptake site with high affinity and the 5-HT uptake site with somewhat lower affinity. 相似文献
193.
194.
Western tussock moths (Orgyia vetusta Bdv., Lymantriidae) infest one stand of bush lupine (Lupinus arboreus Sims, Fabaceae) heavily and several other stands very lightly at the Bodega Marine Reserve (Sonoma Co., Calif., USA). We found that the disappearance rates of experimentally placed larvae and pupae were consistently lower in the outbreak area than in non-outbreak areas. For pupae but not larvae, this difference was removed by using tanglefoot to repel nonflying predators. However, the major nonflying predator of pupae, the ant Formica lasioides, was no more abundant in non-outbreak areas than in the outbreak area. We found inverse density-dependence in the rate of attack by F. lasioides on experimental pupae, suggesting this generalist predator is satiated within the outbreak area, but preys more heavily on the moth where the moth is sparse. 相似文献
195.
196.
A wild type strain ofVerticillium lecanii and a mutant strain with increased tolerance to the fungicide benomyl were evaluated in greenhouse experiments for effects on Heterodera glycines populations. Nematodes were applied at 300 eggs and juveniles per 4,550-cm³ pot (two soybean plants in 4,990 g loamy sand per pot) and at both 300 and 10,000 eggs and juveniles per 1,720-cm³ pot (one soybean plant in 2,060 g sand per pot). With 300 nematodes added per pot, both V. lecanii strains significantly reduced nematode populations in loamy sand (fungus applied at 0.02% dry weight per dry weight loamy sand) and sand (0.006% and 0.06% fungus application rates). The mutant strain applied at 0.002% to sand also significantly reduced cyst numbers. When 10,000 nematodes were added per pot, only the mutant strain at 0.06% significantly decreased population. Various media were tested for isolation of the fungus strains from prills, loamy sand, and sand, but the fungi were recovered from few of the greenhouse pots. 相似文献
197.
Hydroxyl Radical-Mediated Oxidation of Serotonin: Potential Insights into the Neurotoxicity of Methamphetamine 总被引:1,自引:1,他引:0
Monika Z. Wrona Zhaoliang Yang Michelle McAdams Susan O'Connor-Coates Glenn Dryhurst 《Journal of neurochemistry》1995,64(3):1390-1400
Abstract: When incubated with a hydroxyl radical (HO?)-generating system (ascorbic acid/Fe2+-EDTA/O2/H2O2), 5-hydroxytryptamine (5-HT; serotonin) is rapidly oxidized initially to a mixture of 2,5-, 4,5-, and 5,6-dihydroxytryptamine (DHT). The major reaction product is 2,5-DHT, which at physiological pH exists as its keto tautomer, 5-hydroxy-3-ethylamino-2-oxindole (5-HEO). Rapid autoxidation of 4,5-DHT gives tryptamine-4,5-dione (T-4,5-D), which reacts with the C(3)-centered carbanion of 5-HEO to give 3,3′-bis(2-aminoethyl)-5-hydroxy-[3,7′-bi-1H-indole]-2,4′,5′-3H-trione (7). The latter slowly cyclizes to 3′-(2-aminoethyl)-1′,6′,7′,8′-tetrahydro-5-hydroxyspiro[3H-indole-3,9′-[9H]pyrrolo[2,3-f]quinoline]-2,4′,5′(1H)- trione (9). A minor amount of T-4,5-D dimerizes to give 7,7′-bi-(5-hydroxytryptamine-4-one) (7,7′-D). In the presence of GSH, the reaction of T-4,5-D with 5-HEO is diverted and, in the presence of sufficient concentrations of this tripeptide, completely blocked. This is because GSH preferentially reacts with T-4,5-D to give 7-S-glutathionyltryptamine-4,5-dione (11). The results of this investigation suggest that 5,6-DHT, 5-HEO, 7, and 9 are products unique to the HO?-mediated oxidation of 5-HT. Thus, the observation of other investigators that 5,6-DHT is formed in the brains of rats following a large dose of methamphetamine (MA) suggests that this drug might evoke HO? formation. However, the present in vitro study indicates that 5,6-DHT is a rather minor, unstable product of the HO?-mediated oxidation of 5-HT and suggests that detection of 5-HEO, 7/9, and 11 in rat brain following MA administration could provide additional support for HO? formation. Furthermore, one or more of the intermediates and major products of oxidation of 5-HT by HO? might, in addition to 5,6-DHT, contribute to the MA-induced degeneration of serotonergic neurons. 相似文献
198.
Susan J. Holt Peter Alexander Chris B. Inman Donna E. Davies 《Experimental cell research》1995,217(2)
Ligand-induced translocation of epidermal growth factor receptors (EGF-R) to the nucleus of NR6/HER fibroblasts has been studied by immunoelectron microscopy. Following treatment of NR6/HER cells with epidermal growth factor (EGF) for 1 h, there was a decrease in EGF-R labeling at the plasma membrane and a corresponding increase in EGF-R in the nucleus. This was preceded by a rapid and sustained increase in nuclear phosphotyrosine content, detectable within 2 min of EGF treatment. EGF-R translocation into the nucleus was completely prevented by 18 h serum starvation prior to treatment with EGF. These results indicate that translocation of EGF-R to the nucleus is a controlled process and they suggest theft EGF-R may directly influence nuclear function. 相似文献
199.
200.
B. D. Metscher R. Glenn Northcutt David M. Gardiner Susan V. Bryant 《Development genes and evolution》1997,207(5):287-295
Gene expression has been studied in considerable detail in the developing vertebrate brain, neural crest, and some placode-derived
organs. As a further investigation of vertebrate head morphogenesis, expression patterns of several homeobox-containing genes
were examined using whole-mount in situ hybridization in a sensory system primitive for the vertebrate subphylum: the axolotl
lateral lines and the placodes from which they develop. Axolotl Msx-2 and Dlx-3 are expressed in all of the lateral line placodes. Both genes are expressed throughout development of the lateral line system
and their expression continues in the fully developed neuromasts. Expression within support cells is highly polarized. In
contrast to most other observations of Msx genes in vertebrate organogenesis, expression of Msx-2 in developing lateral line organs is exclusively epithelial and is not associated with epithelial-mesenchymal interactions.
A Hox-complex gene, Hoxb-3, is shown to be expressed in the embryonic hindbrain and in a lateral line placode at the same rostrocaudal level, but not
in other placodes nor in mature lateral line organs. A Hox gene of a separate paralog group, Hoxa-4, is expressed in a more posterior hindbrain domain in the embryo, but is not expressed in the lateral line placode at that
rostrocaudal level. These data provide the first test of the hypothesis that the neurogenic placodes develop in two rostrocaudal
series aligned with the rhombomeric segments and patterned by combinations of Hox genes in parallel with the central nervous system.
Received: 2 April 1997 / Accepted: 2 July 1997 相似文献