全文获取类型
收费全文 | 47980篇 |
免费 | 6119篇 |
国内免费 | 21795篇 |
出版年
2024年 | 208篇 |
2023年 | 1359篇 |
2022年 | 2208篇 |
2021年 | 2832篇 |
2020年 | 2669篇 |
2019年 | 3089篇 |
2018年 | 2185篇 |
2017年 | 1977篇 |
2016年 | 2222篇 |
2015年 | 3029篇 |
2014年 | 4058篇 |
2013年 | 3772篇 |
2012年 | 5080篇 |
2011年 | 4906篇 |
2010年 | 3807篇 |
2009年 | 3851篇 |
2008年 | 4115篇 |
2007年 | 3810篇 |
2006年 | 3544篇 |
2005年 | 3012篇 |
2004年 | 2299篇 |
2003年 | 1985篇 |
2002年 | 1777篇 |
2001年 | 1665篇 |
2000年 | 1508篇 |
1999年 | 1020篇 |
1998年 | 566篇 |
1997年 | 414篇 |
1996年 | 348篇 |
1995年 | 289篇 |
1994年 | 238篇 |
1993年 | 215篇 |
1992年 | 218篇 |
1991年 | 193篇 |
1990年 | 174篇 |
1989年 | 131篇 |
1988年 | 153篇 |
1987年 | 115篇 |
1986年 | 118篇 |
1985年 | 121篇 |
1984年 | 86篇 |
1983年 | 60篇 |
1982年 | 97篇 |
1981年 | 46篇 |
1980年 | 16篇 |
1979年 | 30篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1957年 | 22篇 |
1950年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
R Liang 《Biochemical and biophysical research communications》1984,120(3):741-746
Primary cell cultures were prepared from breast muscles of 11 day 4 hour-embryonic chicks. Cytoplasmic RNAs were isolated from the cultured cells at various time intervals from day 3 to day 8. A [P32] DNA probe complementary to messenger RNA of myosin heavy chain was used to hybridize with the RNAs after gel electrophoresis. A transient species of polyadenylated RNA with a decreased mobility in electrophoresis was detected during a period of time when contractions of syncytial fibers were first observed. 相似文献
2.
3.
HAN-QI YANG HONG WANG DE-ZHU LI 《Botanical journal of the Linnean Society. Linnean Society of London》2008,156(3):411-423
The foliage leaf epidermis of 35 species representing 12 key genera of woody bamboos of the Asian tropics was investigated using light and scanning electron microscopy. The results indicated that papillae forms and distributional patterns around the stomatal apparatus of the abaxial foliage leaf epidermis were usually constant and were of great taxonomic significance at the specific and generic levels. However, papillae characters were not suitable for dividing subtribes within woody bamboos of the Asian tropics. On the basis of papillae characters, Schizostachyum s.s. and Cephalostachyum were confirmed, but their delimitations should be modified. The transfer of Leptocanna chinensis and Schizostachyum sanguineum into Cephalostachyum was supported, and Cephalostachyum virgatum and C . pergracile were confirmed to be members of Schizostachyum s.s. The subtribe Racemobambosinae did not obtain support and Racemobambos appeared to be better placed in subtribe Bambusinae. Neomicrocalamus was supported as a close relative and better treated as a synonym of Racemobambos . Gigantochloa was closely related to Dendrocalamus . © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 411–423. 相似文献
4.
WANG JC 《The Journal of general physiology》1948,31(3):259-268
1. Experiments were performed on six dogs to determine the rate of penetration of Cl(33) and Na(24) across the blood-aqueous humor and blood-cerebrospinal fluid barriers after intravenous injection of the radioactive ions. The radioactivity measurements were made with an immersion type of Geiger-Müller counter. 2. The concentrations of the labelled ions in the anterior chamber and the cisterna magna increase slowly to approach that of plasma. The rate of penetration k is calculated from a simple exponential equation with the half-value interval t(0.5) or the time required for the labelled-ion concentration in the fluid to reach 50 per cent of that of plasma. The average t(0.5) for Cl(38) and Na(24) in aqueous humor are 34.3 +/- 9 and 27.3 +/- 9 minutes, respectively, while those for cerebrospinal fluid are 90 +/- 6 and 95 +/- 6 minutes, respectively. 3. A study of the radioactivity in plasma was made to determine the per cent remaining after a steady state was reached. By means of this determination the sodium and chloride space was calculated to be 33 +/- 5 per cent. 相似文献
5.
6.
7.
8.
9.
10.
XIAO-YUAN HE SHI-JUN WANG JASON HILTON fls YI-LONG ZHOU 《Botanical journal of the Linnean Society. Linnean Society of London》2006,151(2):279-288
Several isolated marattialean synangia and sporangia are reported from coal balls collected from Coal Seam No.1 (C605) in the uppermost Permian Wangjiazhai Formation in Guizhou Province, south-western China. The synangia are radially symmetrical with diameters between 0.8 and 1.2 mm and are 1.7 mm long, consisting of 3–4 elongate sporangia that are fused basally, free distally and possess a pointed apex. The outer-facing sporangial wall is 4–5 cells thick and conspicuously differentiated. Spores are trilete, have a granular ornamentation and are nearly round equatorially with a diameter of 55–60 µm. Comparisons with other anatomically preserved Palaeozoic marattialean synangia from the Euramerican and Cathaysian floras permit their assignment to the genus of Scolecopteris (Zenker) Millay. In this species the thick, outer-facing sporangial walls and large trilete spores are features consistent with those of the Oliveri Group within Scolecopteris , a group that has previously been considered primitive within this genus. Distinctions from all other previously recognized species within the Oliveri Group lead to the creation of a new species, S. guizhouensis sp. nov. This species is the youngest of the reported species of Scolecopteris recognized from the Euramerican and Cathaysian floras, and provides important evidence on the organization of marattialean ferns from the Upper Permian strata of south China. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 279–288. 相似文献