全文获取类型
收费全文 | 319520篇 |
免费 | 15776篇 |
国内免费 | 861篇 |
出版年
2021年 | 1869篇 |
2019年 | 1743篇 |
2018年 | 14628篇 |
2017年 | 13388篇 |
2016年 | 11036篇 |
2015年 | 3986篇 |
2014年 | 4943篇 |
2013年 | 6883篇 |
2012年 | 12005篇 |
2011年 | 20904篇 |
2010年 | 17622篇 |
2009年 | 13038篇 |
2008年 | 17041篇 |
2007年 | 18824篇 |
2006年 | 7706篇 |
2005年 | 7456篇 |
2004年 | 8063篇 |
2003年 | 7808篇 |
2002年 | 7498篇 |
2001年 | 9600篇 |
2000年 | 9196篇 |
1999年 | 7086篇 |
1998年 | 2191篇 |
1997年 | 2027篇 |
1996年 | 1862篇 |
1992年 | 5531篇 |
1991年 | 5770篇 |
1990年 | 5706篇 |
1989年 | 5656篇 |
1988年 | 5258篇 |
1987年 | 4897篇 |
1986年 | 4473篇 |
1985年 | 4711篇 |
1984年 | 3725篇 |
1983年 | 3065篇 |
1982年 | 2036篇 |
1981年 | 1746篇 |
1979年 | 3382篇 |
1978年 | 2597篇 |
1977年 | 2395篇 |
1976年 | 2350篇 |
1975年 | 2848篇 |
1974年 | 3129篇 |
1973年 | 3095篇 |
1972年 | 3012篇 |
1971年 | 2886篇 |
1970年 | 2237篇 |
1969年 | 2179篇 |
1968年 | 2054篇 |
1967年 | 1809篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
T. B. Lapirova V. R. Mikryakova A. S. Mavrin G. A. Yinogradova 《Journal of Evolutionary Biochemistry and Physiology》2000,36(1):47-51
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon
exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic
character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and
structural-functional organization of the studied organs. 相似文献
24.
25.
Z Zhong A Toukdarian D Helinski V Knauf S Sykes J E Wilkinson C O'Bryne T Shea C DeLoughery R Caspi 《Applied and environmental microbiology》2001,67(12):5771-5779
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results. 相似文献
26.
Y. Salas A. Márquez J. Canelón Y. Perazzo V. Colmenárez J. A. López 《Mycopathologia》2012,174(5-6):511-517
Pythium insidiosum is a pathogenic oomycete known since 1890 that causes pythiosis in mammals. In this report, seven P. insidiosum isolates were recovered from Venezuelan horses and were characterized. The strains were recovered from biopsied tissues and kunkers collected from granulomatous masses located on the hind limb and from a nodular lesion in the left upper eyelid, which decrease the ability of the horses to be used for working purposes. The methods used to identify P. insidiosum isolates were based on the production of sporangia and zoospores, histopathology and PCR assay. To further characterize these strains, portions of the 18S rRNA genes of the seven isolates were sequenced. The sequences showed high homology to previously described P. insidiosum DNA sequences available in GenBank. Similar studies based on the morphological, histological and molecular data identified the etiological agent in samples of granulomatous lesions in these equines as P. insidiosum. In America, the infection has been diagnosed more frequently in equines of Brazil, Colombia, Costa Rica and the United States of America. 相似文献
27.
Self-consistent steady-state axisymmetric configurations of a plasma envelope with a uniform anisotropic conductivity around a rotating magnetized spherical body are considered. A set of electrodynamic and magnetohydrodynamic equations is analyzed under the assumption that the mass velocity of a moving weakly ionized plasma has only the azimuthal component. The equations describing the profile of the angular frequency of the rotating plasma envelope, the magnetic field, the conduction currents, and the plasma density distribution are solved in the limit of a strong anisotropy of the conductivity of a weakly ionized gas. The applicability of the results obtained to a qualitative interpretation of the phenomena occurring in the plasmaspheres of magnetized planets is discussed. 相似文献
28.
I. N. Semenchuk L. A. Taranova A. A. Kalenyuk P. V. Il’yasov A. N. Reshetilov 《Applied Biochemistry and Microbiology》2000,36(1):69-72
The operating and storage stability of a receptor element of an amperometric biosensor based on thePseudomonas rathonis strain T capable of degrading surfactants was tested. Microbial cells were immobilized by incorporation in gels (agar, agarose,
and calcium-alginate), polyvinyl alcohol membrane, adhesion to Chromatographic paper GF/A, or by cross-linking induced by
glutaric aldehyde. Incorporation of microbial cells in agar gel provides long-standing conservation of their activity and
viability during measurements of high concentrations of surfactants and allows the receptor element of the biosensor to be
rapidly recovered after measurements. 相似文献
29.
D S Faffe G H Silva P M Kurtz E M Negri V L Capelozzi P R Rocco W A Zin 《Journal of applied physiology》2001,90(4):1400-1406
The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung. 相似文献
30.
V. Grant 《Plant Systematics and Evolution》2001,230(1-2):89-96
This paper deals with the use of cladistic methods and cladograms in phylogeny reconstruction in plant groups containing
numerous taxa. How accurate are the cladograms as to details? Accuracy tests at the level of details require an independently
known phylogeny, which excludes most plant groups, but such tests can be carried out in domesticated and experimental plant
groups which have documented pedigrees. Four such tests are known and are presented here: a new case in Gilia and three previously published cases in Avena, Hordeum, and Helianthus. The four cases include domesticated and experimental plants, use of morphological and molecular evidence, and presence of
dichotomous as well as reticulate phylogenies. The cladograms of the four plant groups all differ in significant details from
the known pedigrees. These results are discussed in relation to problems of interpretation of cladograms.
Received March 21, 2000 Accepted August 16, 2001 相似文献