全文获取类型
收费全文 | 12365篇 |
免费 | 873篇 |
国内免费 | 117篇 |
出版年
2023年 | 106篇 |
2022年 | 121篇 |
2021年 | 314篇 |
2020年 | 233篇 |
2019年 | 250篇 |
2018年 | 481篇 |
2017年 | 378篇 |
2016年 | 520篇 |
2015年 | 550篇 |
2014年 | 628篇 |
2013年 | 931篇 |
2012年 | 1033篇 |
2011年 | 981篇 |
2010年 | 627篇 |
2009年 | 494篇 |
2008年 | 537篇 |
2007年 | 477篇 |
2006年 | 484篇 |
2005年 | 304篇 |
2004年 | 290篇 |
2003年 | 274篇 |
2002年 | 243篇 |
2001年 | 175篇 |
2000年 | 176篇 |
1999年 | 195篇 |
1998年 | 125篇 |
1997年 | 110篇 |
1996年 | 103篇 |
1995年 | 128篇 |
1994年 | 105篇 |
1993年 | 72篇 |
1992年 | 101篇 |
1991年 | 95篇 |
1990年 | 75篇 |
1989年 | 89篇 |
1988年 | 80篇 |
1987年 | 84篇 |
1986年 | 65篇 |
1985年 | 89篇 |
1984年 | 67篇 |
1983年 | 78篇 |
1982年 | 74篇 |
1981年 | 82篇 |
1980年 | 64篇 |
1979年 | 73篇 |
1978年 | 57篇 |
1977年 | 65篇 |
1975年 | 55篇 |
1974年 | 49篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The effect of lake restoration measures on the physical,chemical and phytoplankton variables of Lake Bled 总被引:2,自引:2,他引:0
Monthly changes of physical, chemical and biological variables due a combination of artificial inflow of clean water, removal of hypolimnetic water, and diversion of sewage were studied in Lake Bled from December 1980 to December 1982.During the winter period 1981/82 the species composition of the phytoplankton changed. New species replaced those observed in previous years. We conclude that the combined effect of these three lake restoration measures was responsible for the sudden disappearance ofOscillatoria rubescens D.C. A marked decrease in some nutrients and an increase in temperature and oxygen concentration also occurred. 相似文献
82.
83.
Summary Complex carbohydrates in secretory granules and at the apical cell surface of mouse gastric mucoid cells were studied during embryogenesis and in the early postnatal period by various cytochemical methods; the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) and tannic acid-uranyl acetate (TA-UA) procedures made neutral mucosubstances (NMS) visible, whereas the hexose residues of glycoconjugates were identified using WGA-, RCA II- and ConA-ferritin. The glycocalyx was stained with ruthenium red (RR). During differentiation of the embryonic mucoid cells the number of secretory granules increased in parallel to the increase in their carbohydrate component. NMS-stainable parts in secretory granules also had binding sites for the conjugates RCA II- and WGA-ferritin, but the binding of ConA could not be identified. The increasing quantity of NMS in secretory granules was correlated with the increased amount of PA-TCH-SP and TA-UA positive substances in the apical glycocalyx only in 14- and 18-day-old embryos. The observed uniform affinity for RR and lectin conjugates in all analysed developmental stages remains to be explained. 相似文献
84.
František Šťastný Václav Lisý Hana Tomášová Stanislav Trojan 《Neurochemical research》1985,10(6):819-828
Posthypoxic fluctuations in the levels of two excitatory amino acids, glutamate and aspartate, may be related to changes in mechanisms(s) which are responsible for their reuptake. As gamma-glutamyl transpeptidase (GGT) plays a role in mediating the uptake of glutamate and aspartate into various compartments of the brain, we studied changes in the activity of this enzyme in main regions of the brain in young and adult rats. We found a posthypoxic increase in bound GGT activity in some brain regions of 18-day-old animals after acute exposure, but no changes were observed after prolonged altitude hypoxia, with the exception of a decrease in cortical GGT activity. In contrast, acute hypoxia decreased GGT activity in the cortical capillaries to 59%, but prolonged hypoxic exposure was ineffective. However, the activity of soluble GGT in the cerebrospinal fluid of both groups of rats was several-times elevated in comparison with controls. At the same time, bound GGT activity was increased in the liver after acute or prolonged altitude hypoxia. The soluble GGT activity in plasma was only increased after prolonged exposure. Ninety days after prolonged hypoxic exposure the bound GGT activity was reduced in all brain regions to about 60–70% of controls (significantly higher in females than in males) as long-term developmental sequel from early postnatal hypoxia. 相似文献
85.
Krunica Hruška 《Folia Geobotanica》1985,20(3):225-243
A survey of the nitrophilous fringe communities of the region Marche (Central Italy) allows the individualization of five associations well characterized floristically and ecologically. These are:Urtico-Aegopodietum, Anthriscetum sylvestris, Chaerophylletum aurei, Alliario-Chaerophylletum temuli, andAnthriscetum nemorosae. The first three associations are ranged, from the phytosociological point of view, in the allianceAegopodion podagrariae, while the last two belong to the allianceGalio-Alliarion. 相似文献
86.
Glucose inhibits the inducible synthesis of β-D-glucosidase inStreptomyces granaticolor. Neither cAMP nor cGMP influence the inhibitory effect of glucose. Glucose also inhibits the inducible synthesis of the cellobiose
uptake system but has no effect on its activity. This may be the mechanism underlying glucose inhibition of induction of β-D-glucosidase inS.granaticolor. 相似文献
87.
The nucleotide sequence of a rat liver glutathione S-transferase subunit cDNA clone 总被引:17,自引:0,他引:17
We have determined the nucleotide sequence of a cloned cDNA derived from liver poly(A) RNA of pentobarbital-treated rats encoding a glutathione S-transferase subunit. This cDNA clone pGTR261 contains one open reading frame of 222 amino acids, a complete 3' noncoding region, and 63 nucleotides in the 5' noncoding region. The cloned DNA hybridizes to rat poly(A) RNA in a tissue-specific fashion, with strong signals to liver and kidney poly(A) RNA(s) of approximately 1100 and approximately 1400 nucleotides in size but little or no hybridization to poly(A) RNAs from heart, lung, seminal vesicles, spleen, or testis under stringent conditions. Our sequence covers the cDNA sequence of pGST94 which contains a partial coding sequence for a liver glutathione S-transferase subunit of Ya size. Comparison of sequences with our earlier clone pGTR112 suggests that there are at least two mRNA species coding for two different subunits of the Ya (Mr = 25,600) subunit family with very limited amino acid substitutions mainly of conserved polarity. The divergent 3' noncoding sequences should be useful molecular probes in differentiating these two different but otherwise very similar subunits in induction and genomic structure analyses. Our results suggest that tissue-specific expression of the glutathione S-transferase subunits represented by the sequences of pGTR261 and pGTR112 may occur at or prior to the level of RNA processing. 相似文献
88.
89.
The Yc and Ya subunits of rat liver glutathione S-transferases are the products of separate genes 总被引:7,自引:0,他引:7
90.