全文获取类型
收费全文 | 41689篇 |
免费 | 3072篇 |
国内免费 | 11篇 |
专业分类
44772篇 |
出版年
2023年 | 267篇 |
2022年 | 257篇 |
2021年 | 499篇 |
2020年 | 495篇 |
2019年 | 498篇 |
2018年 | 983篇 |
2017年 | 880篇 |
2016年 | 1457篇 |
2015年 | 2121篇 |
2014年 | 2107篇 |
2013年 | 2772篇 |
2012年 | 3768篇 |
2011年 | 3448篇 |
2010年 | 1972篇 |
2009年 | 1568篇 |
2008年 | 2733篇 |
2007年 | 2623篇 |
2006年 | 2540篇 |
2005年 | 2203篇 |
2004年 | 2165篇 |
2003年 | 1997篇 |
2002年 | 1834篇 |
2001年 | 736篇 |
2000年 | 823篇 |
1999年 | 478篇 |
1998年 | 312篇 |
1997年 | 180篇 |
1996年 | 214篇 |
1995年 | 232篇 |
1994年 | 193篇 |
1993年 | 173篇 |
1992年 | 183篇 |
1991年 | 149篇 |
1990年 | 128篇 |
1989年 | 127篇 |
1988年 | 103篇 |
1987年 | 75篇 |
1986年 | 81篇 |
1985年 | 107篇 |
1984年 | 136篇 |
1983年 | 77篇 |
1982年 | 97篇 |
1981年 | 82篇 |
1980年 | 80篇 |
1979年 | 75篇 |
1978年 | 62篇 |
1976年 | 76篇 |
1975年 | 58篇 |
1974年 | 63篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Antonio Balas Felix Garcia-Sanchez Fernando Gomez-Reino Jose L. Vicario 《Immunogenetics》1994,39(6):452-452
Correspondence to: J. L. Vicario. 相似文献
32.
André Brack 《Origins of life and evolution of the biosphere》1993,23(1):3-10
Liquid water has many peculiarities which confer special properties. The most important among them probably are the ability to establish hydrogen bonds, a high polarity and a high dielectric constant. In the presence of liquid water, large organic molecules have to manage the conflict between hydrophobic groups and hydrophilic groups. This duality can generate interesting prebiotic situations such as the stereoselective aggregation of short peptide sequences of alternating hydrophobic — hydrophilic residues into thermostable -sheets endowed with chemical acrivity. Liquid water is also a powerful hydrolytic agent. As such, it allows pathways which would have few chances to occur in an organic solvent.Presented at the Session Water in the Solar System and Its Role in Exobiology during the 26th General Assembly of the European Geophysical Society, 22–26 April 1991 in Wiesbaden, Germany. 相似文献
33.
Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium
José L. Copa-Patiño Young G. Kim Paul Broda 《Applied microbiology and biotechnology》1993,40(1):69-76
We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (Vmax) of the system was 3.86 units (U) mg–1 protein with arabinoxylan as substrate and the substrate concentration giving half Vmax (S0.5) was 0.52 mg ml–1. At concentrations of arabinoxylan greater than 15 mg ml–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components.
Correspondence to: P. Broda 相似文献
34.
The wind cooling effect determines wind chill equivalent-temperatures, which may be rather different to actual temperature. In a windy region such as Patagonia, this difference may reach a magnitude and persistence to become an important bioclimatic element. This paper quantifies the wind cooling effect in Patagonia by the presentation of equivalent isotherms as an adaptation of the usual isotherm maps to the regional bioclimatic environment. It is concluded that due to seasonal variations in wind speed, the annual equivalent temperature range is smaller than the actual temperature range, thus increasing oceanic features, from a thermal viewpoint, of the Patagonian climate.«Les vents que chassent, à travers une échancrure de la Cordillère des Andes, les hautes pressions du Pacifique, s'étranglent et s'accelèrent dans un étroit couloir de cent kilomètres de front, en direction de l'Atlantique, et raclent tout sur leur passage».Antoine de Saint-Exupéry «Un sens à la vie» (1956) 相似文献
35.
Neuza Domingues André R. A. Marques Rita Diogo Almeida Calado Inês S. Ferreira Cristiano Ramos José Ramalho Maria I. L. Soares Telmo Pereira Luís Oliveira José R. Vicente Louise H. Wong Inês C. M. Simões Teresa M. V. D. Pinho e Melo Andrew Peden Cláudia Guimas Almeida Clare E. Futter Rosa Puertollano Winchil L. C. Vaz Otília V. Vieira 《Traffic (Copenhagen, Denmark)》2023,24(7):284-307
36.
A thorough analysis of glass containing Eu2O3 and Dy2O3, or Eu2O3, Dy2O3, and CuO melted together with nanodiamond powder was pursued based on measurements of optical absorption, photoluminescence (PL) emission and excitation spectra, and colorimetry. Nanodiamond facilitated the stabilization of Cu+ and Eu2+ ions with blue-emitting characteristics that, along with yellow-emitting Dy3+ and red-emitting Eu3+ led to the white light-emitting glass. Novel intensity notations implemented in intensity-based spectral ratios, and difference intensity correlation analysis were proposed for the assessment of PL properties. The chromaticity and correlated colour temperature of the emission were ultimately investigated as a two-parametric problem based on: (1) the different ionic components; and (2) the various excitation wavelengths employed. The optical analysis approach adds to the characterization methods to further fundamental understanding and provide helpful analytical tools for designing materials for tunable white light-emitting devices. 相似文献
37.
Juan José R. Coque Juan F. Martín Paloma Liras 《Molecular genetics and genomics : MGG》1993,236(2-3):453-458
38.
The lifeform and the biological production of pure stands ofEichhornia azurea Kunth in three lakes in tropical Brazil were studied. The lifeform ofE. azurea is termed ‘semi-emergent’, because the plant has well developed trailing stems just under the water, and the aerial lamina
emerges with the thick petiole. The density of shoot apices was 9.9, 17.2 and 17.1 m−2 in Lake Dom Helvecio, Lake Jacaré and Lake Carioca, respectively. The mean daily increment of the apical shoot biomass was
between 1.8 and 4.8 g m−2 day−1. The mean leaf life-span in Lake Dom Helvecio, Lake Jacaré and Lake Carioca was estimated to be 78, 49 and 64 days in the
wet season and 73, 70 and 73 days in the dry season, respectively. The stem life-span was estimated to be about 28 months.
Starch content in the current years' stem ranged from 24 to 118 mg g−1 dry matter with fluctuations, the amplitude of which decreased with age. The differences for most of the growth parameters,
such as density of shoot apices, daily increment of biomass and leaf life-span, between dry and wet season are smaller than
those among the three lakes. Both the decrease in daily dry matter production and the increase in leaf life-span occurred
in order from Lake Dom Helvecio to Lake Jacaré and Lake Carioca. The low productivity ofE. azurea is considered to be related to a low leaf area index, a long time interval for the emergence of new leaves, long leaf life-span
and a low capacity for branching. 相似文献
39.
Coelho-Rocha Nina Dias de Jesus Luís Cláudio Lima Barroso Fernanda Alvarenga Lima da Silva Tales Fernando Ferreira Enio Gonçalves José Eduardo dos Santos Martins Flaviano de Oliveira Carvalho Rodrigo Dias Barh Debmalya Azevedo Vasco Ariston de Carvalho 《Probiotics and antimicrobial proteins》2023,15(1):160-174
Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,... 相似文献
40.
Maria J. P. van Dongen Sybren S. Wijmenga Ramón Eritja Fernando Azorín Cornelis W. Hilbers 《Journal of biomolecular NMR》1996,8(2):207-212
Summary A new application of the HMBC experiment is presented that provides a useful means to discriminate between H2 and H8 proton resonances, to assign the base proton resonances to the various residue types and, most importantly, to correlate the H2 and H8 protons for adenine or inosine residues in natural abundance 13C fragments. The utility of this experiment is demonstrated for an unlabeled DNA 20-mer. Thanks to the obtained results, preliminary conclusions could be drawn regarding the molecular conformations of the non-canonical G/I-A base pairs in the hairpin formed by this fragment. 相似文献