全文获取类型
收费全文 | 21147篇 |
免费 | 1850篇 |
国内免费 | 5篇 |
专业分类
23002篇 |
出版年
2023年 | 89篇 |
2022年 | 239篇 |
2021年 | 442篇 |
2020年 | 237篇 |
2019年 | 319篇 |
2018年 | 433篇 |
2017年 | 370篇 |
2016年 | 657篇 |
2015年 | 1054篇 |
2014年 | 1209篇 |
2013年 | 1454篇 |
2012年 | 1807篇 |
2011年 | 1699篇 |
2010年 | 1100篇 |
2009年 | 959篇 |
2008年 | 1296篇 |
2007年 | 1332篇 |
2006年 | 1147篇 |
2005年 | 1091篇 |
2004年 | 1070篇 |
2003年 | 979篇 |
2002年 | 932篇 |
2001年 | 237篇 |
2000年 | 189篇 |
1999年 | 183篇 |
1998年 | 248篇 |
1997年 | 172篇 |
1996年 | 147篇 |
1995年 | 139篇 |
1994年 | 127篇 |
1993年 | 116篇 |
1992年 | 103篇 |
1991年 | 97篇 |
1990年 | 102篇 |
1989年 | 71篇 |
1988年 | 65篇 |
1987年 | 73篇 |
1986年 | 61篇 |
1985年 | 59篇 |
1984年 | 63篇 |
1983年 | 75篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1980年 | 52篇 |
1979年 | 43篇 |
1978年 | 61篇 |
1977年 | 46篇 |
1976年 | 44篇 |
1974年 | 52篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Models of the visual cortex are based on image decomposition according to the Fourier spectrum (amplitude and phase). On one hand, it is commonly believed that phase information is necessary to identify a scene. On the other hand, it is known that complex cells of the visual cortex, the most numerous ones, code only the amplitude spectrum. This raises the question of knowing if these cells carry sufficient information to allow visual scene categorization. In this work, using the same experiments in computer simulation and in psychophysics, we provide arguments to show that the amplitude spectrum alone is sufficient for categorization task. 相似文献
992.
Bai Y Galetskiy D Damoc E Paschen C Liu Z Griese M Liu S Przybylski M 《Proteomics》2004,4(8):2300-2309
In the present study, one- and two-dimensional gel electrophoresis combined with high resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) have been applied as powerful approaches for the proteome analysis of surfactant proteins SP-A and SP-D, including identification of structurally modified and truncation forms, in bronchoalveolar lavage fluid from patients with cystic fibrosis, chronic bronchitis and pulmonary alveolar proteinosis. Highly sensitive micropreparation techniques were developed for matrix-assisted laser desorption/ionization (MALDI) FT-ICR MS analysis which provided the identification of surfactant proteins at very low levels. Owing to the high resolution, FT-ICR MS was found to provide substantial advantages for the structural identification of surfactant proteins from complex biological matrices with high mass determination accuracy. Several protein bands corresponding to SP-A and SP-D were identified by MALDI-FT-ICR MS after electrophoretic separation by one- and two-dimensional gel electrophoresis, and provided the identification of structural modifications (hydroxy-proline) and degradation products. The high resolution mass spectrometric proteome analysis should facilitate the unequivocal identification of subunits, aggregations, modifications and degradation products of surfactant proteins and hence contribute to the understanding of the mechanistic basis of lung disease pathogenesis. 相似文献
993.
Damgaard C 《Comptes rendus biologies》2004,327(3):255-260
Neighbouring plants generally compete for the limiting resources in order to grow and reproduce. Some resources, e.g., sun light, may be monopolised by the larger plants and this may lead to asymmetric competition where a plant, which is twice as large, grows more than twice as fast. A previously published individual-based Richards growth model that describes the asymmetric growth of individual plants is here generalised with respect to a variable mean plant density and an explicit spatial setting. 相似文献
994.
The present study contrasts available biological data and results of morphofunctional analyses of the bill and hyoid apparatus in motmots. It shows that these omnivorous birds, which take relatively large food items, possess osteomuscular peculiarities that enable them to process these items as a whole in order to soften or cut them, and make them suited for easy ingestion. For that, they use the crenate edges of their rhamphotheca. Their jaws work as a highly mobile saw-like system. Their mutual movements, enhanced by the fact that particular dispositions of the hyoid apparatus rise the tongue and the supported items high up into buccal cavity, facilitate an effective clamping of items that can be moved along the jaws and be quite appropriately processed. 相似文献
995.
996.
NMR structure of the bovine prion protein isolated from healthy calf brains 总被引:5,自引:0,他引:5 下载免费PDF全文
NMR structures of recombinant prion proteins from various species expressed in Escherichia coli have been solved during the past years, but the fundamental question of the relevancy of these data relative to the naturally occurring forms of the prion protein has not been directly addressed. Here, we present a comparison of the cellular form of the bovine prion protein isolated and purified from healthy calf brains without use of detergents, so that it contains the two carbohydrate moieties and the part of the GPI anchor that is maintained after enzymatic cleavage of the glycerolipid moiety, with the recombinant bovine prion protein expressed in E. coli. We show by circular dichroism and (1)H-NMR spectroscopy that the three-dimensional structure and the thermal stability of the natural glycoprotein and the recombinant polypeptide are essentially identical. This result indicates possible functional roles of the glycosylation of prion proteins in healthy organisms, and provides a platform and validation for future work on the structural biology of prion proteins, which will have to rely primarily on the use of recombinant polypeptides. 相似文献
997.
How does parkin ligate ubiquitin to Parkinson's disease? 总被引:6,自引:0,他引:6
Recessive mutations in the human PARKIN gene are the most common cause of hereditary parkinsonism, which arises from the degeneration of dopaminergic neurons in the substantia nigra. However, the molecular mechanisms by which the loss of parkin causes dopaminergic neurodegeneration are not well understood. Parkin is an enzyme that ubiquitinates several candidate substrate proteins and thereby targets them for proteasomal degradation. Hypothesis-driven searches have led to the discovery of aggregation-prone protein substrates of parkin. Moreover, the enzyme is upregulated when under unfolded protein stress. Thus, loss-of-function mutations of parkin might impair the removal of potentially toxic protein aggregates. However, the limited neuropathological information that is available from parkin-proven patients, as well as the recent knockout of the parkin gene in fruit flies and mice, may indicate a more complex disease mechanism, possibly involving the misfolding of parkin itself or of additional substrates. The risk factors that predispose dopaminergic neurons to degenerate on parkin failure are yet to be identified. 相似文献
998.
999.
The new methods of laser microdissection microscopy have received wide acceptance in biology and have been applied in a small number of parasitology investigations. Here, the techniques and applications of laser microdissection microscopy are reviewed with suggestions of how the systems might be used to explore applied questions in parasite molecular biology and host-parasite interactions. 相似文献
1000.
Kienberger Ferry Zhu Rong Moser Rosita Rankl Christian Blaas Dieter Hinterdorfer Peter 《Biological procedures online》2004,6(1):120-128
Dynamic force microscopy (DFM) allows imaging of the structure and the assessment of the function of biological specimens
in their physiological environment. In DFM, the cantilever is oscillated at a given frequency and touches the sample only
at the end of its downward movement. Accordingly, the problem of lateral forces displacing or even destroying bio-molecules
is virtually inexistent as the contact time and friction forces are reduced. Here, we describe the use of DFM in studies of
human rhinovirus serotype 2 (HRV2) weakly adhering to mica surfaces. The capsid of HRV2 was reproducibly imaged without any
displacement of the virus. Release of the genomic RNA from the virions was initiated by exposure to low pH buffer and snapshots
of the extrusion process were obtained. In the following, the technical details of previous DFM investigations of HRV2 are
summarized.
Published: June 29, 2004. 相似文献