全文获取类型
收费全文 | 1324篇 |
免费 | 351篇 |
国内免费 | 200篇 |
专业分类
1875篇 |
出版年
2025年 | 14篇 |
2024年 | 24篇 |
2023年 | 46篇 |
2022年 | 66篇 |
2021年 | 60篇 |
2020年 | 79篇 |
2019年 | 74篇 |
2018年 | 71篇 |
2017年 | 63篇 |
2016年 | 69篇 |
2015年 | 55篇 |
2014年 | 79篇 |
2013年 | 110篇 |
2012年 | 51篇 |
2011年 | 106篇 |
2010年 | 60篇 |
2009年 | 103篇 |
2008年 | 84篇 |
2007年 | 80篇 |
2006年 | 58篇 |
2005年 | 55篇 |
2004年 | 49篇 |
2003年 | 64篇 |
2002年 | 44篇 |
2001年 | 37篇 |
2000年 | 36篇 |
1999年 | 39篇 |
1998年 | 22篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1875条查询结果,搜索用时 15 毫秒
1.
A convenient synthesis of [1-14C]-mono-trans fatty acid using olefin inversion as a key-step is described. This methodology allows for a facile synthesis of [1-14C]-labelled mono-trans analogues of oleic, linoleic and linolenic acids. As an example, only eleven steps were necessary to obtain the [1-14C]-mono-E isomers of linolenic acid from its commercial all-Z form. In the first step, Barton's decarboxylation procedure yielded a bromo intermediate. Epoxidation of this compound resulted in the formation of three monoepoxides, which could be separated by HPLC. After identification by 1H NMR and MS, the pure monoepoxides were then subjected to inversion consisting of a stereospecific deoxygenation followed by a beta-elimination step. Finally, the labelling was introduced by substitution of the bromine by a [14C]-cyano group followed by hydrolysis. 相似文献
2.
Carbon-source assimilation pattern of the astaxanthin-producing yeast Phaffia rhodozyma 总被引:7,自引:0,他引:7
Palágyi Zs. Ferenczy L. Vágvölgyi Cs. 《World journal of microbiology & biotechnology》2001,17(1):95-97
Eleven Phaffia rhodozyma strains were assayed for their ability to utilize 99 compounds as single carbon source. Some of them showed modified coloration compared to colonies of the same strain grown on glucose medium. 相似文献
3.
H. Llaneza Coalla J.M. Blanco FernándezM.A. Morís Morán M.R. López Bobo 《Bioresource technology》2009,100(17):3843-3847
In view of the pressing problem that appears in our region (Asturias, north of Spain) with the residues from the cider production, it was decided to test this kind of material as a co-substrate joint with slaughterhouse waste in a laboratory unit. 相似文献
4.
Binding of arachidonic acid to myeloid-related proteins (S100A8/A9) enhances phagocytic NADPH oxidase activation 总被引:1,自引:0,他引:1
Activation of the O(2)(-) generating NADPH oxidase of phagocytes results from the assembly of the membrane-bound flavocytochrome b(558) with cytosolic proteins, p67(phox), p47(phox), and Rac. However, it has been recently reported that the arachidonic acid- and calcium-binding heterodimer S100A8/A9, abundant in neutrophil cytosol, influences the activation process. In a semi-recombinant system comprising neutrophil membranes, recombinant proteins, p67(phox), p47(phox), GTPgamma S-loaded Rac2, and arachidonic acid (AA), both the rate and the extent of the oxidase activation were increased by S100A8/A9, provided it was preloaded with AA. Binding of [(14)C]AA to S100A8/A9 was potentiated by recombinant cytosolic phox proteins and GTPgammaS, suggesting the formation of a complex, comprising oxidase activating proteins and S100A8/A9, with a greater affinity for AA. The rate constant of oxidase activation was not increased by AA-loaded S100A8/A9, whereas the maximal oxidase activity elicited was twice as high. AA-loaded S100A8/A9 increases oxidase activation probably by decreasing the deactivation rate. 相似文献
5.
Payyavula RS Tay KH Tsai CJ Harding SA 《The Plant journal : for cell and molecular biology》2011,65(5):757-770
6.
Yanhai Yin Shizhong Li Yiming Chen Hongqing Guo Wenzhong Tian Ying Chen Liangcai Li 《Plant Cell, Tissue and Organ Culture》1993,32(1):61-68
Calluses were induced from immature embryos of an indica type rice and finely dispersed cell suspension cultures were initiated from the callus using modified AA medium (S1 medium). The suspension cultures were maintained alternatively (1–2 passages in each medium) in S1 medium and S2 medium, the latter containing KNO3, NH4NO3, proline and glutamine as nitrogen source. Protoplasts of high quality were isolated form suspension cells cultured in S2 medium supplemented with ABA. Embedding the protoplasts in agarose blocks containing NH4NO3-free modified KM8P(PM1) medium and immersing the blocks in NH4NO3-containing modified KM8P(PM3) medium were most effective for obtaining protoplast division and callus formation. The protoplast-derived calluses were precultured in potato extract-aand/or ABA-containing N6(D1, D2 or D3) media and many embryo-like structures were formed. These structures developed into plantlets after being transferred to N6 differentiation (D4) medium. The regenerated plantlets grew into mature plants and beard seeds normally.Abbreviations AA medium
amino acids based medium
- ABA
abscisic acid
- BA
benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- DF
division frequency
- IAA
indoleacetic acid
- KIN
kinetin
- NAA
naphthaleneacetic acid
- PE
planting efficiency 相似文献
7.
Yuan-Fu Deng Shi-Di Tang Liang-Qiang Lao Shu-Zhong Zhan 《Inorganica chimica acta》2010,363(4):827-7300
Pure nanocrystallite magnesium titanate (MgTiO3) was conveniently synthesized by thermal decomposition of a cheap and water-soluble heterobimetallic single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]·7H2O at low temperature. This single source precursor was obtained in high yield and in a crystalline form from the quaternary system of MgO-Ti(OC4H9)4-H2O2-H3nta (H3nta = nitrilotriacetic acid) at pH 4.0. It was characterized by elemental analysis, IR spectrum, NMR, thermal gravimetric analysis and X-ray single-crystal diffraction. The morphology, microstructure, and crystallinity of the resulting MgTiO3 materials have been characterized by transmission electron microscopy and X-ray diffraction. The TEM image of the resulting MgTiO3 powders only consists of the nano-scale crystallites with the crystalline size of 30-100 nm. 相似文献
8.
Manganese (Mn) is an essential element for humans, animals, and plants and is required for growth, development, and maintenance of health. Studies show that Mn metabolism is similar to that of iron, therefore, increased Mn levels in humans could interfere with the absorption of dietary iron leading to anemia. Also, excess exposure to Mn dust, leads to nervous system disorders similar to Parkinson's disease. Higher exposure to Mn is essentially related to industrial pollution. Thus, there is a benefit in developing a clean non-invasive technique for monitoring such increased levels of Mn in order to understand the risk of disease and development of appropriate treatments.To this end, the feasibility of Mn measurements with their minimum detection limits (MDL) has been reported earlier from the McMaster group. This work presents improvement to Mn assessment using an upgraded system and optimized times of irradiation and counting for induced gamma activity of Mn. The technique utilizes the high proton current Tandetron accelerator producing neutrons via the 7Li(p,n)7Be reaction at McMaster University and an array of nine NaI (Tl) detectors in a 4π geometry for delayed counting of gamma rays. The neutron irradiation of a set of phantoms was performed with protocols having different proton energy, current and time of irradiation. The improved MDLs estimated using the upgraded set up and constrained timings are reported as 0.67 μgMn/gCa for 2.3 MeV protons and 0.71 μgMn/gCa for 2.0 MeV protons. These are a factor of about 2.3 times better than previous measurements done at McMaster University using the in vivo set-up. Also, because of lower dose-equivalent and a relatively close MDL, the combination of: 2.0 MeV; 300 μA; 3 min protocol is recommended as compared to 2.3 MeV; 400 μA; 45 s protocol for further measurements of Mn in vivo. 相似文献
9.
Concerns over water quality in Ireland have increased in recent years, in part due to the more frequent contamination of drinking water by pathogens such as Escherichia coli and Cryptosporidium. The objective of this study was to assess the use of SWAT for pathogen source estimation and to analyze the effects of various source scenarios on pathogen outputs in Irish catchments. Two agricultural catchments in Ireland susceptible to pathogen contamination of source water were the center of the SWAT model development with the primary focus on levels of E. coli in surface water. Model simulations used site and source specific information which was analyzed considering the total E. coli count for the simulation period (Fergus: January 2005–October 2006; Kilshanvey: January 2006–July 2007). Pathogen source estimation identified point sources as the most significant contributors to E. coli output with direct deposition the primary contributor (95%) in Kilshanvey and wastewater treatment plant outflow (89%) the main contributor in the Fergus catchment. A scenario analysis evaluated possible situations that may occur in study locations. The analysis indicated that restriction of livestock access to water sources and improved wastewater treatment would represent effective methods of improving water quality in both catchments. 相似文献
10.
Callus cultures from 300 genotypes of alfalfa (Medicago sativa L.) were initiated from leaf, petiole, and internode explants placed on Blaydes medium containing 10.74 M -naphthaleneacetic acid, 11.42 M indole-3-acetic acid, and 9.29 M kinetin. Five genotypes produced somatic embryos. Upon transfer of these embryos to growth regulator-free Murashige and Skoog medium with B5 vitamins, new somatic embryos repeatedly formed directly on older somatic embryos without an intervening callus phase in a cycle lasting about 30 days. These cultures have been maintained for two years, during which time their embryogenic capacity has remained stable. New embryogenic cultures could be started repeatedly from these genotypes. The elimination of sugars from the medium could stop recurrent embryogenesis. Glucose, maltose, and fructose stimulated recurrent embryogenesis more effectively than sucrose. Sucrose was superior to lactose, while sorbitol and mannitol did not stimulate recurrent somatic embryogenesis. The absence of nicotinic acid in the medium, as long as sucrose was present, was lethal to embryos of three of the five tested genotypes. The ability of this system to propagate embryos exponentially offers potential for development of new gene transfer systems and application to artificial seed technology.Abbreviations NAA
-naphthaleneacetic acid
- RSE
recurrent somatic embryogenesis 相似文献