全文获取类型
收费全文 | 20611篇 |
免费 | 1635篇 |
国内免费 | 2141篇 |
出版年
2024年 | 32篇 |
2023年 | 416篇 |
2022年 | 544篇 |
2021年 | 743篇 |
2020年 | 798篇 |
2019年 | 971篇 |
2018年 | 921篇 |
2017年 | 636篇 |
2016年 | 685篇 |
2015年 | 697篇 |
2014年 | 1080篇 |
2013年 | 1715篇 |
2012年 | 806篇 |
2011年 | 1095篇 |
2010年 | 827篇 |
2009年 | 1046篇 |
2008年 | 1096篇 |
2007年 | 1081篇 |
2006年 | 912篇 |
2005年 | 893篇 |
2004年 | 658篇 |
2003年 | 576篇 |
2002年 | 593篇 |
2001年 | 516篇 |
2000年 | 399篇 |
1999年 | 320篇 |
1998年 | 310篇 |
1997年 | 306篇 |
1996年 | 290篇 |
1995年 | 315篇 |
1994年 | 314篇 |
1993年 | 273篇 |
1992年 | 228篇 |
1991年 | 207篇 |
1990年 | 220篇 |
1989年 | 180篇 |
1988年 | 137篇 |
1987年 | 125篇 |
1986年 | 142篇 |
1985年 | 211篇 |
1984年 | 240篇 |
1983年 | 139篇 |
1982年 | 158篇 |
1981年 | 120篇 |
1980年 | 74篇 |
1979年 | 98篇 |
1978年 | 71篇 |
1977年 | 78篇 |
1976年 | 47篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 59 毫秒
91.
Abstract A microcosm using rotating slate discs in a chemostat was used to study bacterial population dynamics and genetic interactions in river epilithon. Populations of all introduced donor and recipient Pseudomonas spp. decreased with time but all the bacteria survived better on the slate discs than in the liquid phase. Conjugal transfer of an epilithic plasmid encoding mercury resistance (pQM1) occured with transfer frequencies of 1.4 × 10−6 to 3.6 × 10−3 per recipient, which were about 100-fold lower than in standard membrane filter mating experiments. 相似文献
92.
Aquaspirillum magnetotacticum MS-1 cells cultured microaerobically (dissolved O2 tension 1% of saturation), expressed proteins with superoxide dismutase (SOD) activity. The majority (roughly 95%) of total cell superoxide dismutase activity was located in the cell periplasm with little or no activity in the cell cytoplasm. Irontype SOD (FeSOD) contributed 88% of the total activity activity detected, although a manganese-type SOD (MnSOD) was present in the periplasm as well. Cells cultured at a higher dissolved O2 tension (10% of saturation) expressed increased activity of the MnSOD relative to that of the FeSOD. 相似文献
93.
94.
In order to investigate the reliability of the Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) for trace
element analysis of biological materials, we have carried out extensive investigations on human plasma, using an Applied Research
Laboratory’s ICP-AES. When we aspirated the untreated plasma into the spectrometer, we obtained unreliable and nonreproducible
results. However, when we pretreated the plasma by wet digestion (to destroy all the organic material), we achieved reproducible
and consistent results. It is, therefore, suggested that biological samples should be pretreated, preferably by wet digestion,
before being aspirated into the ICP-AES for analysis. 相似文献
95.
Because the acrosome of human sperm is too small to be directly visualized by phase-contrast microscopy, acrosome reactions (that is loss of the acrosome) are generally not evaluated in studies of human sperm capacitation and fertilization. Nevertheless, it would be useful in such studies to have a technique for easily identifying and quantitating acrosome-reacted sperm. In this paper, we describe a method for labeling the human sperm acrosome with fluorescein-conjugated Ricinus communis agglutinin-60 (FITC-RCA); we show that in sperm without acrosomal caps, FITC-RCA labeling occurs either not at all or only in the equatorial segment of the acrosome. To determine if the absence of FITC-RCA labeling in the acrosomal cap region gives a reliable estimate of acrosome reactions, washed sperm or sperm incubated in a capacitating medium (BWW) were divided into two groups, which were then fixed for FITC-RCA labeling or transmission electron microscopy. Counts of acrosome reactions made by each method were similar, and we observed an increase in the percentage of reactions following incubation in BWW. We conclude that the FITC-TCA labeling technique is a reliable method for accurately scoring the percentage of acrosome-reacted human sperm. 相似文献
96.
Nataly Mancette Rijensky Netta R. Blondheim Shraga Eilon Barnea Nir Peled Eli Rosenbaum Aron Popovtzer Solomon M. Stemmer Alejandro Livoff Mark Shlapobersky Neta Moskovits Dafna Perry Eitan Rubin Itzhak Haviv Arie Admon 《Molecular & cellular proteomics : MCP》2020,19(8):1360-1374
Highlights
- •Sufficient tumor tissues are often unavailable large HLA peptidome discovery.
- •Using patient derived xenograft (PDX) tumors can overcome this limitation.
- •The large PDX HLA peptidomes expand significantly those of the original biopsies.
- •The HLA peptidomes of the PDX tumors included many tumor antigens.
97.
Thomas Bell Michael B. Bonsall Angus Buckling Andrew S. Whiteley Timothy Goodall Robert I. Griffiths 《Biology letters》2010,6(5):639-642
Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity–diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity–diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators. 相似文献
98.
《Molecular & cellular proteomics : MCP》2020,19(3):518-528
Highlights
- •Discovery of peptide biomarker candidates of respiratory tract pathogens S. pneumoniae, H. influenzae, M. catarrhalis and S. aureus as target pathogens.
- •Peptide biomarker candidates were experimentally verified in clinical samples.
- •Targeted MS using promising peptide biomarker candidates shown as proof-of-concept.
99.
Synthesis and in vitro bioactivity of C-terminal deleted analogs of human growth hormone-releasing factor 总被引:4,自引:0,他引:4
N Ling A Baird W B Wehrenberg N Ueno T Munegumi P Brazeau 《Biochemical and biophysical research communications》1984,123(2):854-861
A series of C-terminal deleted analogs of human growth hormone-releasing factor (hGRF) with either an amidated or a free carboxylic acid C-terminus were synthesized by solid phase methodology. Their capacity to release growth hormone was tested on rat anterior pituitary cells in monolayer culture. A gradual decrease of bioactivity down to 23% relative to hGRF was noted when the C-terminal amino acids were deleted to hGRF (1-34)OH. Further deletions, however, did not decrease the bioactivity because the potencies of the fragments, hGRF(1-31)NH2, (1-30)NH2 and (1-29)NH2 remained at about 50% of that of hGRF. Continual deletion of residues to hGRF(1-23)NH2, (1-22)NH2 and (1-21)NH2 still yielded bioactive fragments with full intrinsic activity despite very low potency. Only with the deletion down to hGRF(1-19)NH2 did the bioactivity completely disappear. Thus, together with the data published in a previous paper (1), the minimal biologically active core of hGRF with full intrinsic activity comprises the fragment (3-21). 相似文献
100.