全文获取类型
收费全文 | 3041篇 |
免费 | 335篇 |
国内免费 | 3篇 |
专业分类
3379篇 |
出版年
2021年 | 26篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 62篇 |
2015年 | 84篇 |
2014年 | 99篇 |
2013年 | 141篇 |
2012年 | 143篇 |
2011年 | 148篇 |
2010年 | 97篇 |
2009年 | 103篇 |
2008年 | 133篇 |
2007年 | 123篇 |
2006年 | 146篇 |
2005年 | 137篇 |
2004年 | 130篇 |
2003年 | 118篇 |
2002年 | 109篇 |
2001年 | 53篇 |
2000年 | 34篇 |
1999年 | 57篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 51篇 |
1994年 | 54篇 |
1993年 | 54篇 |
1992年 | 63篇 |
1991年 | 48篇 |
1990年 | 46篇 |
1989年 | 46篇 |
1988年 | 34篇 |
1987年 | 42篇 |
1986年 | 54篇 |
1985年 | 59篇 |
1984年 | 50篇 |
1983年 | 28篇 |
1982年 | 33篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 43篇 |
1978年 | 31篇 |
1977年 | 23篇 |
1976年 | 27篇 |
1975年 | 20篇 |
1974年 | 24篇 |
1973年 | 25篇 |
1970年 | 33篇 |
1968年 | 19篇 |
排序方式: 共有3379条查询结果,搜索用时 15 毫秒
41.
William D. Figg Herman J.C. Yeh Alain Thibault James M. Pluda Fumio Itoh Robert Yarchoan Michael R. Cooper 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1994,652(2)
This paper describes a reversed-phase, high-performance liquid chromatographic (HPLC) method for the isolation, detection, and quantification of TNP-470 (I) and one of its active metabolites, AGM-1883 (II), from plasma. These compounds are initially extracted from plasma with an organic solvent and then separated from one another on a C18 column. Those fractions eluting from the C18 column and containing either I or II are then derivatized through their epoxide moieties with sodium 8-quinolinethiolate (SQT). This derivatization produces fluorescent species that are isolated and quantified by a second reversed-phase HPLC analysis. The assay yields a lower limit of reliable quantification of 2.5 ng/ml and is linear to a concentration at least as high as 160 ng/ml. The inter-assay percent coefficient of variation is less than 18%. 相似文献
42.
Lawrence Cris W.; Little Pamela A.; Little Brian W.; Glushka John; van Halbeek Herman; Alhadeff Jack A. 《Glycobiology》1993,3(3):249-259
The N-glylycans have been removed by peptide-N-glycosidase F(PNGase F) from purified human non-secretory RNases derivedfrom kidney, liver and spleen. The spleen RNase was purifiedby two procedures, one of which did not include the usual acidtreatment step (0.25 M H2SO4, 45 min, 4C), to determine ifacid treatment alters the carbohydrate moieties. TheN-glycansof the RNases were fractionated by Bio-Gel P-4 chromatographyand analysed by 600 MHz 1H-NMR spectroscopy and electrospraymass spectrometry. All four non-secretory RNase preparationscontained the following structures: The relative amounts of the trisaccharide, pentasaccharide andhexasaccharide appeared to vary slightly in the different tissueRNases. The overall results indicate: (i) that acid treatmentduring purification does not alter the N-glycans of non-secretoryRNases; (ii) that the N-glycans from kidney, liver and spleennon-secretory RNases are very similar, if not identical, toone another, but different from the N-glycan structures reportedfor secretory RNase. N-glycans non-secretory RNases 相似文献
43.
Estimating estuarine residence times in the Westerschelde (The Netherlands) using a box model with fixed dispersion coefficients 总被引:13,自引:6,他引:7
The residence time of the water masses in the Westerschelde estuary was determined using a simple compartment-model that simulates the advective-diffusive transport of a conservative dissolved substance (chlorinity). The residence time of a water parcel in the upstream part of the estuary (i.e. the time needed for this water parcel to leave the estuary) varied from about 50 days in winter to about 70 days in summer. The most seaward compartment had residence times of about 10-15 days.Dispersive coefficients that are fixed in time were able to reproduce the observed salinity distributions very well in the Westerschelde. They were obtained by calibration on observed chlorinities. It is argued that the apparent relationship of dispersive coefficients with freshwater flow, which is observed in certain studies, could (partly) reflect the deviation from steady state conditions which are required assumptions to calculate these dispersive coefficients directly from salinity profiles. 相似文献
44.
A ncl-1 mutation results in enlarged nucleoli, which can be detected in nearly all cells of living animals by Nomarski microscopy. Spontaneous mitotic loss of a ncl-1(+)-containing free duplication in an otherwise homozygous ncl-1 mutant animal results in mosaicism for ncl-1 expression, and the patterns of mosaicism lead us to conclude that ncl-1 acts cell autonomously. The probability of mitotic loss of the duplication sDp3 is approximately constant over many cell divisions. About 60% of the losses of sDp3 at the first embryonic cell division involve nondisjunction. Frequencies of mitotic loss of different ncl-1(+)-bearing free duplications varied over a 200-fold range. The frequencies of mitotic loss were enhanced by a chromosomal him-10 mutation. We have used ncl-1 as a cell autonomous marker in the mosaic analysis of dpy-1 and lin-37. The focus of action of dpy-1 is in hypodermis. A mutation in lin-37 combined with a mutation in another gene results in a synthetic multivulva phenotype. We show that lin-37 acts cell nonautonomously and propose that it plays a role, along with the previously studied gene lin-15, in the generation of an intercellular signal by hyp7 that represses vulval development. 相似文献
45.
46.
Comparison of purified anti-actin and fluorescent-heavy meromyosin staining patterns in dividing cells 总被引:15,自引:7,他引:8 下载免费PDF全文
We purified actin antibodies by affinity chromatography from the serum of rabbits immunized with glutaraldehyde-fixed chicken gizzard actin filaments and used this anti-actin to localize actin in myofibrils and fixed cultured cells at each stage of the cell cycle. By double immunodiffusion the anti-actin reacted with both smooth and skeletal muscle actin. Several blocking and absorption experiments demonstrated that the antibodies also bound specifically to actin in nonmuscle cells. The same structures stained using either the direct or the indirect fluorescent antibody technique; and, while the indirect method was more sensitive, the direct method was superior because there was no detectable nonspecific staining. As expected, anti-actin stained the I-band of myofibrils. It also stained stress fibers and membrane ruffles in HeLa cells. Some PtK-2 cells have straight stress fibers which stained with anti-actin, but in confluent cultures all PtK-2 cells have, instead, sinuous phase-dense fibers which stained with antibody. At prophase the whole cytoplasm stained uniformly with anti-actin. During metaphase and anaphase, anti-actin staining was concentrated diffusely in the mitotic spindle. In contrast, fluorescent heavy meromyosin stained discrete fine spindle fibers in these fixed cells. During cytokinesis, anti-actin stained the whole cytoplasm uniformly and was not concentrated in the cleavage furrow. 相似文献
47.
Leo Pine Herman Gross Georgia Bradley Malcolm James R. George S. B. Gray C. Wayne Moss 《Mycopathologia》1977,61(3):131-141
Two strains of Histoplasma capsulatum were required to prepare maximum yields of H and of M antigen from histoplasmin. The antigens were separated and partially purified by a series of procedures yielding an overall recovery of 70 to 90% of the individual antigens. Stable products suitable for use as reference products were obtained when the final purification step employed DEAE-cellulose with phosphate buffer elution at increasing molarity and decreasing pH. A final step of purification of each antigen with slab acrylamide gel electrophoresis gave products which were highly reactive and specific in a variety of serological tests with sera from persons with proven cases of histoplasmosis and with natural infections of heterologous deep mycoses. These antigens were maximally active at concentrations of 2 to 16 g protein in the complement fixation, capillary precipitin, microimmunodiffusion, or immunoelectrophoresis tests; 0.5 g gave a maximum delayed cutaneous hypersensitivity reaction in homologously infected animals and caused no appreciable reaction in control animals. Although these antigens appeared to be specific when tested with sera from persons with natural infections, the M and H antigens demonstrated the presence of an additional antigen reacting with sera of rabbits immunized with cell membrane and cell particulate fractions of Blastomyces dermatitidis. After purification by electrophoresis, both the H and M antigens of some preparations showed some decomposition and loss of reactivity after storage at 5 C for more than six months. The overall results suggest that the purified H and M antigens of Heiner (12) have multiple serological reactivity and may function in precipitin reactions, complementfixing reactions, hemagglutination of formalin-fixed goose red blood cells, and as antigens for delayed cutaneous tests. 相似文献
48.
The occurrence of larval Anisakis in North Sea herring was examined during the period 1965-1972 using a sampling method which yielded comparable data for all eight years. Data on abundance of infestation in several herring stocks pointed to remarkable fluctuations over the study period with an increase in the period 1966-1968 followed by a decrease in the period 1968-1972. Of various hypotheses that may explain this situation, it is concluded that changes in the migration behaviour of the herring may be responsible. Other data and statistics are discussed with special reference to variations in infestation level in different samples and to the occurrence of adult nematodes in marine mammals. 相似文献
49.
50.
L A Moore M J Arrizubieta W E Tidyman L A Herman E Bandman 《Journal of molecular biology》1992,225(4):1143-1151
cDNAs encoding the rod region of four different fast myosin heavy chains (MYCHs) in the chicken were identified, using anti-MYCH monoclonal antibodies, in two expression libraries prepared from 19-day embryonic and adult chicken muscle. These clones were used to determine the amino acid sequences that encompass the epitopes of five anti-MYHC monoclonal antibodies. Additionally, the amino acid sequences were compared to each other and to a full length embryonic MYHC. Although there is extensive homology in the chicken fast myosin rods, sequences within the hinge, within the central portion of the light meromyosin fragment, and at the carboxy terminus exhibit the largest number of amino acid substitutions. We propose that divergence within these subdomains may contribute to isoform-specific properties associated with skeletal myosin rods. 相似文献