全文获取类型
收费全文 | 20146篇 |
免费 | 1556篇 |
国内免费 | 11篇 |
出版年
2023年 | 64篇 |
2022年 | 191篇 |
2021年 | 361篇 |
2020年 | 219篇 |
2019年 | 311篇 |
2018年 | 374篇 |
2017年 | 339篇 |
2016年 | 549篇 |
2015年 | 929篇 |
2014年 | 1051篇 |
2013年 | 1314篇 |
2012年 | 1515篇 |
2011年 | 1417篇 |
2010年 | 938篇 |
2009年 | 863篇 |
2008年 | 1124篇 |
2007年 | 1053篇 |
2006年 | 1076篇 |
2005年 | 1041篇 |
2004年 | 977篇 |
2003年 | 854篇 |
2002年 | 903篇 |
2001年 | 250篇 |
2000年 | 202篇 |
1999年 | 240篇 |
1998年 | 265篇 |
1997年 | 198篇 |
1996年 | 218篇 |
1995年 | 195篇 |
1994年 | 211篇 |
1993年 | 207篇 |
1992年 | 181篇 |
1991年 | 143篇 |
1990年 | 116篇 |
1989年 | 132篇 |
1988年 | 130篇 |
1987年 | 92篇 |
1986年 | 92篇 |
1985年 | 113篇 |
1984年 | 138篇 |
1983年 | 100篇 |
1982年 | 130篇 |
1981年 | 102篇 |
1980年 | 97篇 |
1979年 | 80篇 |
1978年 | 77篇 |
1977年 | 72篇 |
1976年 | 48篇 |
1974年 | 48篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Heat shock protein-mediated resistance to high hydrostatic pressure in Escherichia coli 总被引:1,自引:0,他引:1
Aertsen A Vanoirbeek K De Spiegeleer P Sermon J Hauben K Farewell A Nyström T Michiels CW 《Applied and environmental microbiology》2004,70(5):2660-2666
A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i). the expression of rpoH, encoding the heat shock-specific sigma factor sigma(32), was also induced by high pressure; (ii). heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii). basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels. 相似文献
992.
A series of new iron(III) and copper(II) complexes of bovine serum transferrin (BTf), with carbonate and/or oxalate as the synergistic anion, are presented. The complexes [Fe(2)(CO(3))(2)BTf], [Fe(2)(C(2)O(4))(2)BTf], [Cu(2)(CO(3))(2)BTf] and [Cu(C(2)O(4))BTf] were prepared by standard titrimetric techniques. The oxalate derivatives were also obtained from the corresponding carbonate complexes by anion-displacement. The site-preference of the transition metal-oxalate synergism has facilitated the preparation and isolation of the mononuclear complex [Cu(C(2)O(4))BTf], the mixed-anion complexes [Cu(2)(CO(3))(C(2)O(4))BTf] and [Fe(2)(CO(3))(C(2)O(4))BTf] and the mixed-metal complex [FeCu(C(2)O(4))(2)BTf]. The sensitivity of electron paramagnetic resonance (EPR) spectroscopy to the nature of the synergistic anions at the specific-binding sites of the transferrins has made this physical technique particularly indispensable to this study. None of the other members of the transferrin family of proteins has ever been demonstrated to bind the ferric and cupric ions one after the other, each occupying a separate specific-binding site of the same transferrin molecule, as a response to the coordination restrictions imposed by the oxalate ion. The bathochromic shift of the visible p(pi)-d(pi*) CT band for iron(III)-BTf and the hypsochromic shift of the p(pi)-d(sigma*) CT band for copper(II)-BTf, on replacing carbonate by oxalate as the associated anion, are consistent with the relative positions of these anionic ligands in the spectrochemical series and the nature of the d-type acceptor orbitals involved in the CT transitions. The binding and spectroscopic properties of bovine serum transferrin--a serum transferrin--very nearly mirror those of human serum transferrin, but differ significantly from those of human lactoferrin. 相似文献
993.
de Groot P Weterings K de Been M Wittink F Hulzink R Custers J van Herpen M Wullems G 《Plant molecular biology》2004,55(5):715-726
994.
995.
Ten years after its introduction the Special Admissions to Psychiatric Hospitals Act (Bopz) still awaits full implementation in the field of psychogeriatric nursing home care. Ethnographic research into moral problems related to care giving in dementia patients in Dutch nursing homes yielded several reasons for this discrepancy between law and care practice. Firstly, practical effectuation of this law rests predominantly on the shoulders of nurses and nurse assistants who are mainly inspired by moral motives such as carefulness and providing safety and who are ill informed about the law and its prerequisites. Secondly, there is the problem of the loss of a common shared world of meaning, which in relational terms is typical for the process of dementia. As a result of this, crucial concepts of the Bopz loose their applicability as the disease progresses. Finally, there is an immanent tension between the anthropology of care and care giving and the anthropological presuppositions of the law, health law included, which on a fundamental level contributes to the resistance of the care practice to the legal procedures of the Bopz. These factors must be accounted for in new legislation or revision of the current law. In the mean time we urge the necessity to develop a moral code concerning how to deal with resistive behaviour and opposition to care of demented nursing home patients. 相似文献
996.
Jan Víteček Vojtěch Adam Jiří Petřek Jan Vacek René Kizek Ladislav Havel 《Plant Cell, Tissue and Organ Culture》2004,79(2):195-201
Growth is one of the basic properties of biological systems. The methods which are commonly used for the determination of growth are usually difficult and not very accurate. In the present work we decided to use esterase activity as a growth marker in tobacco suspension culture (BY-2 line) and in early somatic embryos of Norway spruce (clone 2/32) grown on a semi-solid medium. Esterase activity correlates well with the classical growth characteristics of BY-2 and spruce early somatic embryos. Determination of esterase activity is based on spectrophotometric and spectrofluorimetric detection of reaction products, which arise from the enzymatic hydrolysis of two substrates (p -nitrophenyl acetate and fluorescein diacetate) by esterase. The spectrophotometric method enabled us to detect approximately 104 BY-2 cells and 25 spruce embryos whereas the more sensitive spectrofluorimetric method allowed us to detect approximately 800 BY-2 cells and 5 early somatic embryos of Norway spruce. 相似文献
997.
998.
999.
Recognition of protein-DNA binding sites in genomic sequences is a crucial step for discovering biological functions of genomic sequences. Explosive growth in availability of sequence information has resulted in a demand for binding site detection methods with high specificity. The motivation of the work presented here is to address this demand by a systematic approach based on Maximum Likelihood Estimation. A general framework is developed in which a large class of binding site detection methods can be described in a uniform and consistent way. Protein-DNA binding is determined by binding energy, which is an approximately linear function within the space of sequence words. All matrix based binding word detectors can be regarded as different linear classifiers which attempt to estimate the linear separation implied by the binding energy function. The standard approaches of consensus sequences and profile matrices are described using this framework. A maximum likelihood approach for determining this linear separation leads to a novel matrix type, called the binding matrix. The binding matrix is the most specific matrix based classifier which is consistent with the input set of known binding words. It achieves significant improvements in specificity compared to other matrices. This is demonstrated using 95 sets of experimentally determined binding words provided by the TRANSFAC database. 相似文献