全文获取类型
收费全文 | 16281篇 |
免费 | 1251篇 |
国内免费 | 380篇 |
专业分类
17912篇 |
出版年
2023年 | 133篇 |
2022年 | 257篇 |
2021年 | 406篇 |
2020年 | 318篇 |
2019年 | 370篇 |
2018年 | 419篇 |
2017年 | 363篇 |
2016年 | 517篇 |
2015年 | 793篇 |
2014年 | 881篇 |
2013年 | 1108篇 |
2012年 | 1260篇 |
2011年 | 1130篇 |
2010年 | 726篇 |
2009年 | 606篇 |
2008年 | 855篇 |
2007年 | 828篇 |
2006年 | 756篇 |
2005年 | 684篇 |
2004年 | 600篇 |
2003年 | 616篇 |
2002年 | 512篇 |
2001年 | 357篇 |
2000年 | 363篇 |
1999年 | 315篇 |
1998年 | 146篇 |
1997年 | 118篇 |
1996年 | 106篇 |
1995年 | 89篇 |
1994年 | 108篇 |
1993年 | 82篇 |
1992年 | 187篇 |
1991年 | 165篇 |
1990年 | 143篇 |
1989年 | 163篇 |
1988年 | 134篇 |
1987年 | 119篇 |
1986年 | 119篇 |
1985年 | 106篇 |
1984年 | 73篇 |
1983年 | 80篇 |
1982年 | 54篇 |
1981年 | 43篇 |
1980年 | 42篇 |
1979年 | 62篇 |
1977年 | 79篇 |
1976年 | 51篇 |
1975年 | 45篇 |
1974年 | 59篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
A retrovirus carrying the polyomavirus middle T gene induces acute thrombocythemic myeloproliferative disease in mice. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A Fusco G Portella M Grieco G Tajana G Di Minno N Polli A Pinto 《Journal of virology》1988,62(1):361-365
Mice inoculated with an artificially constructed retrovirus carrying the middle T gene of polyomavirus develop acute myeloproliferative disease with severe thrombotic and hemorrhagic disorder and impaired platelet function. The megakaryocytic lineage appears to be a target for polyoma-murine leukemia virus infection and middle T gene expression. This newly described disease represents a unique model system for studying disorders of the megakaryocytic lineage. 相似文献
33.
Pirjo Rajaniemi‐Wacklin Anne Rantala Maria. A. Mugnai Silvia Turicchia Stefano Ventura Jarka Komrkov Liisa Lepist Kaarina Sivonen 《Journal of phycology》2006,42(1):226-232
In this study, the first reported isolates of the genera Snowella and Woronichinia were characterized by 16S rRNA gene sequencing and morphological analysis. Phylogenetic studies and sequences for these genera were not available previously. By botanical criteria, the five isolated strains were identified as Snowella litoralis (Häyrén) Komárek et Hindák Snowella rosea (Snow) Elenkin and Woronichinia naegeliana (Unger) Elenkin. This study underlines the identification of freshly isolated cultures, since the Snowella strains lost the colony structure and were not identifiable after extended laboratory cultivation. In the 16S rRNA gene analysis, the Snowella strains formed a monophyletic cluster, which was most closely related to the Woronichinia strain. Thus, our results show that the morphology of the genera Snowella and Woronichinia was in congruence with their phylogeny, and their phylogeny seems to support the traditional botanical classification of these genera. Furthermore, the genera Snowella and Woronichinia occurred commonly and might occasionally be the most abundant cyanobacterial taxa in mainly oligotrophic and mesotrophic Finnish lakes. Woronichinia occurred frequently and also formed blooms in eutrophic Czech reservoirs. 相似文献
34.
35.
Behavioural expression of D-1 receptor supersensitivity depends on previous stimulation of D-2 receptors 总被引:1,自引:0,他引:1
SKF 38393 (2 mg/kg s.c.), a reportedly selective D-1 agonist, failed to induce contralateral turning behaviour in naive rats bearing 12 days old unilateral 6-hydroxydopamine lesions. On the other hand strong contraversive turning in response to SKF 38393 was obtained if rats had been tested 2 or 7 days before with apomorphine (0.1 mg/kg s.c.) or with LY 171555 (0.2 mg/kg s.c.), a selective D-2 receptor agonist. Contraversive turning in response to SKF 38393 was blocked by a low dose (0.05 mg/kg s.c.) of the specific D-1 antagonist SCH 23390. The results indicate that the behavioural expression of D-1 receptor supersensitivity following lesion of dopaminergic neurons depends on previous exposure to a stimulation of D-2 receptors. 相似文献
36.
37.
38.
The accessibility of DNA to dimethylsulfate in complexes with recA protein. 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
recA protein coats DNA co-operatively to form filaments approximately 100 A thick, which in the presence of ATP, and more stably so in the presence of the non-hydrolyzable analog ATP gamma S, have a helical appearance with a deep cleft in the protein coat. This protein helix follows the DNA helix, to which it imparts a new helicity of 18.5 bp per turn of 97 A pitch. Here we test the accessibility of the DNA in the complex to modification by dimethylsulfate, and find that the complexed DNA is approximately 2-fold more reactive on the major groove side than it was in B-DNA (methylation of guanine N7), while it is protected approximately 2-fold on the minor groove side (methylation of adenine N3), suggesting that the protein coats the DNA along the minor groove. Furthermore, N3 of cytosine, a residue involved in base pairing, is found exposed in complexes with single strands as it is in naked single-stranded DNA, while it remains inaccessible in complexes with double strands, suggesting that the latter is not melted at this stage of the strand exchange reaction. 相似文献
39.
G Del Boccio C Di Ilio E Casalone A Pennelli A Aceto P Sacchetta G Federici 《The Italian journal of biochemistry》1987,36(1):8-17
An anionic (pI 4.6) isoenzyme of glutathione transferase was purified to homogeneity from human thyroid by affinity chromatography followed by isoelectric focusing. The content of enzyme was calculated to constitute about 0.2% of soluble proteins. The enzyme is formed by two identical subunits of 23,000 daltons approximately. The thyroid transferase did not catalyze the reduction of peroxides. Physical, catalytic and immunological analyses demonstrated extensive similarities between the thyroid transferase and the transferase from placenta, erythrocytes and breast. On the other hand, the thyroid transferase appears catalytically different from transferase 7-7, even if both cross-react with the antibodies raised against human placenta transferase. 相似文献
40.
Voltage-dependent activation and inactivation of calcium channels in PC12 cells. Correlation with neurotransmitter release 总被引:10,自引:0,他引:10
F Di Virgilio D Milani A Leon J Meldolesi T Pozzan 《The Journal of biological chemistry》1987,262(19):9189-9195
The existence and mechanisms of inactivation of voltage-gated Ca2+ channels are important, but still debatable, physiological problems. By using the Ca2+ indicators quin2 and fura-2, we demonstrate that in PC12 cells voltage-gated Ca2+ channels undergo inactivation dependent on both voltage and [Ca2+]i. Inactivation, however, is never complete and a small number of channels remains open during prolonged depolarization, explaining the steady state elevation of [Ca2+]i observed in cells depolarized with high KCl. A close parallel exists between Ca2+ channel inactivation and the transient nature of neurotransmitter release: secretion is rapidly stimulated during the first 30 s of depolarization, when a transient overshoot in [Ca2+]i can be demonstrated, while it is negligible during the following period, despite the persistence of an elevated [Ca2+]i; predepolarization in Ca2+-free medium and subsequent addition of Ca2+ (a condition which allows the development of the voltage inactivation) abolishes the fast phase of secretion, while not modifying the steady state [Ca2+]i eventually attained; and increases in the intracellular Ca2+ buffering decreases the amplitude of the fast secretion phase induced by KCl without altering the steady state [Ca2+]i. We suggest that localized [Ca2+]i gradients form close to the plasma membrane shortly after depolarization and that the [Ca2+]i reached in these regions is the relevant parameter in the regulation of secretion. 相似文献