全文获取类型
收费全文 | 97633篇 |
免费 | 471篇 |
国内免费 | 834篇 |
专业分类
98938篇 |
出版年
2024年 | 17篇 |
2023年 | 42篇 |
2022年 | 82篇 |
2021年 | 159篇 |
2020年 | 92篇 |
2019年 | 121篇 |
2018年 | 11940篇 |
2017年 | 10745篇 |
2016年 | 7611篇 |
2015年 | 848篇 |
2014年 | 555篇 |
2013年 | 626篇 |
2012年 | 4616篇 |
2011年 | 13225篇 |
2010年 | 12246篇 |
2009年 | 8424篇 |
2008年 | 10013篇 |
2007年 | 11642篇 |
2006年 | 497篇 |
2005年 | 726篇 |
2004年 | 1172篇 |
2003年 | 1197篇 |
2002年 | 922篇 |
2001年 | 287篇 |
2000年 | 174篇 |
1999年 | 37篇 |
1998年 | 35篇 |
1997年 | 39篇 |
1996年 | 27篇 |
1995年 | 6篇 |
1994年 | 16篇 |
1993年 | 36篇 |
1992年 | 21篇 |
1991年 | 41篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1984年 | 8篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1975年 | 6篇 |
1972年 | 247篇 |
1971年 | 276篇 |
1970年 | 5篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1956年 | 5篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Ricardo Ribeiro Silva Carlos Renato Corso Dácio Roberto Matheus 《World journal of microbiology & biotechnology》2010,26(5):841-846
Estimating fungal growth is important in processes of soil bioremediation. It has been demonstrated that ergosterol is a good
indicator of fungal biomass in solid substrata. In the present study were evaluated the effects upon the ergosterol rate of
Lentinus crinitus Berk. and Psilocybe castanella Peck through the culture conditions of these fungi, which are evaluated for the bioremediation of soils contaminated by organochlorates.
A good correlation between fungal biomass and ergosterol was observed for both species. The culture conditions did not influence
the ergosterol rate of L. crinitus. Yet the ergosterol rate of P. castanella was influenced from 35 days of culture and when grown in the presence of 15.00 g hexachlorobenzene l−1 of culture medium. So it is possible to estimate growth of both species using ergosterol as indicator in processes of soil
bioremediation since the influences observed in the ergosterol rate of P. castanella are considered. 相似文献
72.
There is a special emphasis today on integrating traditional healing within health services. However, most areas in which
there is a system of traditional healing have undergone colonization and a number of pressures suppressing tradition for hundreds
of years. The question arises as to how one can understand today’s tradition in light of earlier traditions. This article
is based on material collected in Sámi areas of Finnmark and Nord-Troms Norway; it compares local healing traditions with
what is known of earlier shamanic traditions in the area. The study is based on 27 interviews among healers and their patients.
The findings suggest that although local healing traditions among the Sámi in northern Norway have undergone major transformations
during the last several hundred years, they may be considered an extension of a long-standing tradition with deep roots in
the region. Of special interest are also the new forms tradition may take in today’s changing global society. 相似文献
73.
This article comprises a literature analysis of 41 river rehabilitation projects to assess the short-term (5 years) ability
of indicator groups to demonstrate progress towards river rehabilitation goals. Positive indications were compared to land-use,
river size, rehabilitation intervention and time. A questionnaire was developed to investigate river manager’s interpretation
of rehabilitation success and to assess their level of adherence to recommendations in the literature with regard to rehabilitation
assessment on a conceptual level. A total of 54 responses were received from respondents based in Germany, The Netherlands
and the United Kingdom. The results indicate that macroinvertebrate indicators, while widely used in assessing river rehabilitation
efforts, exhibited a lower frequency of positive responses than most other indicator types in the short term. Conversely,
terrestrial floodplain indicators exhibited the most frequent level of positive response for all ecological type indicators
leading to recommendations for further investigations into their use for short-term monitoring. Assessment procedures recommended
in literature are largely followed, illustrating the advances that have been made with regard to assessment planning. Indicator
responses are influenced by scale factors, for example, land-use and river size, that are often not considered by rehabilitation
managers. While an emphasis is placed on ecological, hydrological and morphological indicators in monitoring schemes, the
socioeconomic perspective (emphasized in the literature as forming an integral part of the river system) is neglected. 相似文献
74.
75.
The physico-chemical properties of skim milk containing κ-carrageenan (in the concentration range 0–0.06% w/v), flaxseed gum (in the concentration range 0–0.40% w/v), or a mixture of both polysaccharides were studied using dynamic light scattering, under diluted conditions, as well as
in situ, undiluted, using diffusing wave spectroscopy (DWS) and ultrasonic spectroscopy. Flaxseed gum causes phase separation in
milk mixtures, because of thermodynamic incompatibility between the casein micelles and the polysaccharide chains. Confocal
microscopy and ultrasonic spectroscopy showed that while the addition of 0.01% κ-carrageenan was not sufficient to hinder
phase separation, when 0.03% was added, the helix–helix interactions between κ-carrageenan molecules were sufficient to form
a network and stabilize the system. DWS clearly demonstrated that clusters of casein micelles still form even at very low
concentrations of polysaccharides (below the visible phase separation threshold) and that κ-carrageenan hinders visible phase
separation by decreasing the mobility of the casein micelles. 相似文献
76.
Triploid Fritillaria camschatcensis (L.) Ker-Gawler (2n = 3x = 36) is a wild species growing in the low-lying areas of Hokkaido Island, Japan, including the Sapporo campus of Hokkaido
University. Many F. camschatcensis plants grew on the campus about a century ago, but we seldom find the plants nowadays and so a project to restore this species
is being planned. Because preservation of genetic diversity and composition in populations has become a major target of conservation,
this study compared variation in the F. camschatcensis population on the Sapporo campus with that in two other populations in Hokkaido. Phenetic variation assessed by 57 randomly
amplified polymorphic DNA markers showed that the three populations were significantly distinct from each other; analysis
of molecular variance showed 64.3% of variation (P < 0.001) existed among the three populations. Comparison of phenetic diversity on the Sapporo campus population with that
in the two other populations showed that the Sapporo campus population contained large genetic variation despite reduced plant
numbers. These results indicate that multiplying F. camschatcensis individuals on the Sapporo campus is adequate to restore the Sapporo campus population because this population contains enough
genetic diversity, and that transplanting from other populations should be avoided so as not to introduce different genotypes
into the campus. These results will be used to design the restoration strategy. 相似文献
77.
Vaishali A. Kilor Nidhi P. Sapkal Jasmine G. Awari Bharti D. Shewale 《AAPS PharmSciTech》2010,11(1):336-343
In the present study, an attempt was made to prepare immediate-release enteric-coated pellets of aceclofenac, a poorly soluble
nonsteroidal anti-inflammatory drug that has a gastrointestinal intolerance as its serious side effect. Formulation of enteric-coated
pellets with improved solubility of aceclofenac could address both of these problems. To achieve these goals, pellets were
prepared by extrusion–spheronization method using pelletizing agents that can contribute to the faster disintegration and
thereby improve the solubility of the drug. Different disintegrants like β-cyclodextrin, kollidon CL, Ac-Di-Sol, and sodium
starch glycolate were tried in order to further improve disintegration time. The pellets were characterized for drug content,
particle size distribution, flow properties, infrared spectroscopy, surface morphology, disintegration rate, and dissolution
profile. The formulations, which showed best disintegration and dissolution profiles, were coated with Eudragit L100-55, an
enteric-coated polymer which does not dissolve at gastric pH but dissolves at intestinal pH, releasing the drug immediately
in the dissolution medium. The optimized enteric-coated formulation containing 20% κ-carrageenan, lactose, and sodium starch
glycolate as a disintegrant did inhibit the release of the drug for 2 h in 0.1 N HCl, whereas 87% of the drug was released
within 45 min. The improvement was substantial when it was compared with solubility of pure drug under the same conditions.
Thus, dissolution profiles suggested that combination of κ-carrageenan and sodium starch glycolate resulted into fast-disintegrating,
immediate-release pellets, overcoming the bioavailability problem of the poorly soluble drug, aceclofenac, and enteric coating
of these pellets avoids the exposure of aceclofenac to ulcer-prone areas of the gastrointestinal tract. 相似文献
78.
Background
Alpha-synuclein (α-Syn) is a small neuronal protein that has been found to be expressed throughout the brain. It has been shown that α-Syn regulates the homeostasis of monoamine neurotransmitters and is involved in various degenerative and affective disorders. There is indication that α-Syn may regulate expression of the brain-derived neurotropic factor (BDNF) which plays an important role in the mood disorders.Methodology/Principal Findings
The study aimed to analyze the mRNA levels of Snca and Bdnf genes in the ventral tegmental area (VTA) and raphe nuclei of the midbrain in male mice that had each won or defeated 20 encounters (20-time winners and 20-time losers, respectively) in daily agonistic interactions. Groups of animals that had the same winning and losing track record followed by a no-fight period for 14 days (no-fighting winners and no-fighting losers) were also studied. Snca mRNA levels were increased in the raphe nuclei in the 20-time losers and in the VTA of the 20-time winners. After no-fight period Snca mRNA levels decreased in both groups. Snca mRNA levels were similar to the control level in the VTA of the 20-time losers and in the raphe nuclei of the 20-time winners. However Snca gene expression increased in these areas in the no-fighting winners and no-fighting losers in comparison with respective mRNA levels in animals before no-fight period. Bdnf mRNA levels increased in VTA of 20-time winners. Significant positive correlations were found between the mRNA levels of Snca and Bdnf genes in the raphe nuclei.Conclusions/Significance
Social experience affects Snca gene expression depending on brain areas and functional activity of monoaminergic systems in chronically victorious or defeated mice. These findings may be useful for understanding the mechanisms of forming different alpha-synucleinopathies. 相似文献79.
Yasawong M Teshima H Lapidus A Nolan M Lucas S Glavina Del Rio T Tice H Cheng JF Bruce D Detter C Tapia R Han C Goodwin L Pitluck S Liolios K Ivanova N Mavromatis K Mikhailova N Pati A Chen A Palaniappan K Land M Hauser L Chang YJ Jeffries CD Rohde M Sikorski J Pukall R Göker M Woyke T Bristow J Eisen JA Markowitz V Hugenholtz P Kyrpides NC Klenk HP 《Standards in genomic sciences》2010,3(2):126-135
Arcanobacterium haemolyticum (ex MacLean et al. 1946) Collins et al. 1983 is the type species of the genus Arcanobacterium, which belongs to the family Actinomycetaceae. The strain is of interest because it is an obligate parasite of the pharynx of humans and farm animal; occasionally, it causes pharyngeal or skin lesions. It is a Gram-positive, nonmotile and non-sporulating bacterium. The strain described in this study was isolated from infections amongst American soldiers of certain islands of the North and West Pacific. This is the first completed sequence of a member of the genus Arcanobacterium and the ninth type strain genome from the family Actinomycetaceae. The 1,986,154 bp long genome with its 1,821 protein-coding and 64 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project. 相似文献
80.
Bruna Martins Bezerra Antonio da Silva Souto Lewis George Halsey Nicola Schiel 《Journal of Ethology》2008,26(1):175-178
Bradypus variegatus is a member of the Order Pilosa, Family Bradypodidae, and is distributed in many subtropical and tropical countries in South
and Central America. However, studies on this species in the wild are relatively limited and many aspects of its reproductive
behaviour are unknown or unclear. The current report presents new observations of the reproductive behaviour of B. variegatus in its natural environment. These include details of both a male–female copulation and the simultaneous nurturing of two young
sloths. 相似文献