全文获取类型
收费全文 | 39080篇 |
免费 | 3027篇 |
国内免费 | 4篇 |
专业分类
42111篇 |
出版年
2023年 | 321篇 |
2022年 | 425篇 |
2021年 | 867篇 |
2020年 | 669篇 |
2019年 | 854篇 |
2018年 | 1274篇 |
2017年 | 1171篇 |
2016年 | 1523篇 |
2015年 | 1761篇 |
2014年 | 1893篇 |
2013年 | 2639篇 |
2012年 | 3171篇 |
2011年 | 3111篇 |
2010年 | 1920篇 |
2009年 | 1539篇 |
2008年 | 2149篇 |
2007年 | 2036篇 |
2006年 | 1993篇 |
2005年 | 1598篇 |
2004年 | 1611篇 |
2003年 | 1511篇 |
2002年 | 1377篇 |
2001年 | 852篇 |
2000年 | 914篇 |
1999年 | 629篇 |
1998年 | 402篇 |
1997年 | 287篇 |
1996年 | 277篇 |
1995年 | 254篇 |
1994年 | 195篇 |
1993年 | 196篇 |
1992年 | 264篇 |
1991年 | 231篇 |
1990年 | 192篇 |
1989年 | 166篇 |
1988年 | 147篇 |
1987年 | 157篇 |
1986年 | 134篇 |
1985年 | 129篇 |
1984年 | 141篇 |
1983年 | 101篇 |
1982年 | 108篇 |
1981年 | 80篇 |
1980年 | 73篇 |
1979年 | 80篇 |
1978年 | 64篇 |
1977年 | 50篇 |
1975年 | 48篇 |
1974年 | 68篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Tissue culture techniques for the propagation and conservation of endemic or threatened plants can be used to complement the methods usually applied in ex situ conservation. Thus, Minuartia valentina (Caryophyllaceae), an endangered plant species endemic to the Valencia Community (Eastern Spain), was successfully regenerated through shoot proliferation from wild plants growing in their natural area. Nodal segments, 10~mm long, were cut from rametes of adult material, sterilised and established in vitro. Equally successful shoot multiplication was achieved on Murashige and Skoog (MS) medium with 80 mg l-1 phloroglucinol in combination with either 1 mg l-1 6-benzylaminopurine or 1 mg l-1 kinetin. Excised shoots were rooted in MS medium supplemented with an auxin (indole acetic acid, indole-3-butyric acid, or napththalene acetic acid). Shoots rooted well (96–100%) within three weeks in all auxin treatments. However, the use of napththalene acetic acid was discarded because this auxin delayed root differentiation, and induced adventitious root malformation. Rooted plantlets were transferred to pots and 85% of them acclimatized successfully four weeks after transfer to greenhouse conditions, where they exhibited normal morphology and growth. 相似文献
12.
Feasible mechanisms for algal digestion in the king angelfish 总被引:1,自引:0,他引:1
To determine the ability of the king angelfish Holacanthus passer to digest algae, three algal species were immersed in acidic conditions similar to that found in the stomach of fish. Only one of them was not susceptible to acidic lysis; two were affected after 40 and 60 min at pH 2·0. King angelfish have an expanded region of the intestine called here the hindgut chamber (HC) containing populations of micro-organisms. Some of these micro-organisms have the capacity to grow in cellulose, agar, and alginic acid; the main components of algal cell walls. Micro-organisms grew in carboxymethylcellulose cultures under aerobic and micro-aerobic conditions. The HC is highly vascularized, which could increase absorptive efficiency of material digested in it. 相似文献
13.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
14.
F García J Sánchez J Planas 《Comparative biochemistry and physiology. A, Comparative physiology》1987,87(4):947-950
1. Male quails submitted 20 and 120 days to a low iron diet (7 ppm) were compared to female laying quails, exposed for 30 days to the same low iron regime, in order to compare the response of the iron metabolic control under a single (erythropoiesis) or a doubled (erythropoiesis and egg formation) iron demand. 2. Iron deposit in storage organs, the classical hematology and the intestinal iron absorption were analyzed in these animals. 3. In males, after 120 days, the iron deposits were reduced 50 and 75%, but hematological values (hematocrit and hemoglobin concentration) were normal, although in laying quails, after 30 days, an anemic condition was evident in both blood parameters and iron deposits, provoking an iron deficient erythropoiesis. 4. The enhancement of the intestinal iron uptake, confirms the anemic character of these birds. 相似文献
15.
16.
D. Padilla F. Acosta J. A. García F. Real Jose R. Vivas 《Archives of microbiology》2009,191(3):191-198
Hafnia alvei, a Gram negative bacillus related to the Enterobacteriaceae family, is considered an opportunistic pathogen of several animal species and humans. In this communication, we describe
fimbrial-like structures from different strains of H. alvei that cannot be easily ascribed to any of the previously reported fimbrial types in this species (type I or type III). Polymerase
chain reaction (PCR) and immunofluorescence assays were carried out to study fimbriae and flagella in H. alvei strains isolated from different sources. No correlation between the results obtained by PCR and those obtained by phenotypic
methods were found, and the antibodies used gave cross or different recognition patterns of the surface structures present
in these strains. We report as well that strain and growth temperature influence fimbriation and expression of flagella in
human and animal isolates of H. alvei. This study also indicates that the absence of fimbriae have a significant positive influence on the initial adhesion of
H. alvei to human epithelial cells. 相似文献
17.
E. Cortés A.A. Kirk J.A. Goolsby P.J. Moran A.E. Racelis M.A. Marcos-García 《Biocontrol Science and Technology》2011,21(11):1369-1373
Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale. 相似文献
18.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
19.
20.
Halobacterial megaplasmids are negatively supercoiled 总被引:1,自引:0,他引:1
Purificación López-García Josefa Antón Jose Pascua Abad Ricardo Amils 《Molecular microbiology》1994,11(3):421-427
Several covalently closed circular halobacterial megaplasmids (up to more than 500 kb) from different strains of Halolerax mediterranei, have been resolved by orthogonal-field alternating gel electro-phoresis (OFAGE). These molecules seem to be negatively supercoiled in vivo, as deduced from the effect of intercalating agents affecting their topology and, therefore, their electrophoretic mobility. It has also been demonstrated that the topolsomerase II Inhibitor novobiocin affects the native topological state of halobacterial megaplasmids impeding their migration in OFAGE under standard conditions for resolution of large supercoiled molecules. 相似文献