全文获取类型
收费全文 | 9137篇 |
免费 | 1076篇 |
国内免费 | 4篇 |
出版年
2021年 | 98篇 |
2019年 | 103篇 |
2018年 | 102篇 |
2017年 | 96篇 |
2016年 | 142篇 |
2015年 | 282篇 |
2014年 | 280篇 |
2013年 | 332篇 |
2012年 | 462篇 |
2011年 | 471篇 |
2010年 | 287篇 |
2009年 | 247篇 |
2008年 | 397篇 |
2007年 | 442篇 |
2006年 | 389篇 |
2005年 | 373篇 |
2004年 | 364篇 |
2003年 | 334篇 |
2002年 | 367篇 |
2001年 | 239篇 |
2000年 | 228篇 |
1999年 | 190篇 |
1998年 | 110篇 |
1997年 | 107篇 |
1996年 | 103篇 |
1995年 | 98篇 |
1994年 | 94篇 |
1993年 | 96篇 |
1992年 | 131篇 |
1991年 | 151篇 |
1990年 | 143篇 |
1989年 | 133篇 |
1988年 | 150篇 |
1987年 | 117篇 |
1986年 | 110篇 |
1985年 | 132篇 |
1984年 | 159篇 |
1983年 | 106篇 |
1982年 | 125篇 |
1981年 | 99篇 |
1980年 | 81篇 |
1979年 | 103篇 |
1978年 | 96篇 |
1977年 | 86篇 |
1976年 | 87篇 |
1975年 | 76篇 |
1974年 | 110篇 |
1973年 | 93篇 |
1972年 | 73篇 |
1971年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The phylogeny of the fungus gnat family Mycetophilidae (Diptera) is reconstructed with a focus on the species‐rich and taxonomically difficult subfamilies Gnoristinae and Mycomyinae. The multigene phylogenetic analyses are based on five nuclear (18S, 28S, CAD, MCS, ITS2) and four mitochondrial (12S, 16S, COI, CytB) gene markers. The analyses strongly support the monophyly of Mycetophilidae and the subfamilies Manotinae, Sciophilinae, Leiinae, and Mycomyinae, although Gnoristinae is paraphyletic with respect to Mycetophilinae. All the genera and groups of genera included are supported as monophyletic, except for Acomoptera Vockeroth, Boletina Staeger, Dziedzickia Johannsen, Ectrepesthoneura Enderlein, and Neoempheria Osten Sacken. Ancestral character state reconstructions were applied to two morphological features present in Gnoristinae and Mycomyinae (i.e. presence of setae on wing membrane and wing vein R4) in order to assess their evolution. The wing vein R4 appears as an unstable character, spread throughout different clades. A dated phylogeny of the family Mycetophilidae showed that most of the subfamilies of Mycetophilidae originated and diversified during the Cretaceous. The youngest subfamilies, originated in the Paleogene, appear to be Mycomyinae and Mycetophilinae. 相似文献
2.
Difficulties were encountered with the orcein method currently being used to demonstrate hepatitis B surface antigen and copper-associated protein in the liver when a new batch of dye was introduced. A survey of published material produced a plethora of methods with many contradictory recommendations. A number of methods and a variety of orceins were compared to determine which methods and orcein solutions would give the most consistent results. Two methods gave equally satisfactory results and can be recommended for routine use in screening paraffin sections of liver for hepatitis B surface antigen and copper-associated protein. 相似文献
3.
4.
J M Allen J P O'Shea K Mashiter G Williams S R Bloom 《BMJ (Clinical research ed.)》1983,286(6378):1607-1609
Ten patients with advanced progressive adenocarcinoma of the prostate were treated with a long acting analogue of gonadotrophin releasing hormone. Eight of these patients responded to treatment in terms of pain relief and clinical regression of tumour. Serum gonadotrophin and testosterone concentrations were significantly suppressed by the end of the second week of treatment, testosterone concentrations being comparable with those achieved by castration. The two patients who failed to respond had both relapsed previously when receiving conventional treatment, and neither showed any endocrine response to the analogue. Superagonists of gonadotrophin releasing hormone may be the treatment of choice in adenocarcinoma of the prostate, but further trials are required to establish long term safety and efficacy. 相似文献
5.
E. Charles Kerr E Bruce Eaton L. Thomas Netzel 《Nucleosides, nucleotides & nucleic acids》2013,32(5-6):851-866
Abstract Syntheses of two analogs of deoxyuridine with N,N-dialkylaniline chromophores are reported. 5-[3-(N-methylphenylamino)propanoyl]-2′-deoxyuridine (1) and 5-[2-(4-N,N-dimethylaminophenyl)ethyl)]-2′-deoxyuridine (2) are prepared by palladium-mediated coupling. Preparation of 2 was facilitated by in situ transient O4-trimethylsilyl protection during alkynylation which suppressed secondary cyclization of the coupling adduct. 相似文献
6.
Bruce M. Taylor Ronald W. Sarver Gregory Fici Roger A. Poorman Barry S. Lutzke Antonio Molinari Thomas Kawabe Karl Kappenman Allen E. Buhl Dennis E. Epps 《The protein journal》2003,22(1):31-40
The time dependency of the spontaneous aggregation of the fibrillogenic β-Amyloid peptide, Aβ1–40, was measured by turbidity, circular dichroism, HPLC, and fluorescence polarization. The results by all methods were comparable and they were most consistent with a kinetic model where the peptide first slowly forms an activated monomeric derivative (AM), which is the only species able to initiate, by tetramerization, the formation of linear aggregates. The anti-Aβ antibody 6E10, raised against residues 1–17, at concentrations of 200–300 nM delayed significantly the aggregation of 50 μM amyloid peptide. The anti–Aβ antibody 4G8, raised against residues 17–24, was much less active in that respect, while the antibody A162, raised against the C-terminal residues 39–43 of the full-length Aβ was totally inactive at those concentrations. Concomitant with the aggregation experiments, we also measured the time dependency of the Aβ1–40–induced toxicity toward SH-EP1 cells and hippocampal neurons, evaluated by SYTOX Green fluorescence, lactate dehydrogenase release, and activation of caspases. The extent of cell damage measured by all methods reached a maximum at the same time and this maximum coincided with that of the concentration of AM. According to the kinetic scheme, the latter is the only transient peptide species whose concentration passes through a maximum. Thus, it appears that the toxic species of Aβ1–40 is most likely the same transient activated monomer that is responsible for the nucleation of fibril formation. These conclusions should provide a structural basis for understanding the toxicity of Aβ1–40 in vitro and possibly in vivo. 相似文献
7.
8.
Harbor seal ( Phoca vitulina ) haul-out site use may be affected by natural or anthropogenic factors. Here, we use an 11-yr (1997–2007) study of a seal colony located near a mariculture operation in Drakes Estero, California, to test for natural (El Niño-Southern Oscillation (ENSO), density-dependence, long-term trends) and anthropogenic (disturbance or displacement related to oyster production activities) factors that may influence the use of haul-out subsites. Annual mariculture related seal disturbance rates increased significantly with increases in oyster harvest ( r s = 0.55). Using generalized linear models (GLMs) ranked by best fit and Akaike's Information Criteria, ENSO and oyster production (as a proxy for disturbance/displacement) best explained the patterns of seal use at all three subsites near the mariculture operations, with effects being stronger at the two subsites closest to operations. Conversely, density-dependence and linear trend effects poorly explained the counts at these subsites. We conclude that a combination of ENSO and mariculture activities best explain the patterns of seal haul-out use during the breeding/pupping season at the seal haul-out sites closest to oyster activities. 相似文献
9.
10.