全文获取类型
收费全文 | 97726篇 |
免费 | 484篇 |
国内免费 | 910篇 |
专业分类
99120篇 |
出版年
2024年 | 18篇 |
2023年 | 64篇 |
2022年 | 146篇 |
2021年 | 304篇 |
2020年 | 132篇 |
2019年 | 175篇 |
2018年 | 11954篇 |
2017年 | 10764篇 |
2016年 | 7612篇 |
2015年 | 840篇 |
2014年 | 561篇 |
2013年 | 697篇 |
2012年 | 4530篇 |
2011年 | 13116篇 |
2010年 | 12158篇 |
2009年 | 8381篇 |
2008年 | 9952篇 |
2007年 | 11520篇 |
2006年 | 422篇 |
2005年 | 644篇 |
2004年 | 1071篇 |
2003年 | 1101篇 |
2002年 | 865篇 |
2001年 | 310篇 |
2000年 | 221篇 |
1999年 | 70篇 |
1998年 | 37篇 |
1997年 | 37篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 45篇 |
1992年 | 51篇 |
1991年 | 85篇 |
1990年 | 52篇 |
1989年 | 40篇 |
1988年 | 45篇 |
1987年 | 55篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 36篇 |
1983年 | 37篇 |
1982年 | 19篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1975年 | 19篇 |
1973年 | 20篇 |
1972年 | 256篇 |
1971年 | 285篇 |
1962年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
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
83.
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
84.
85.
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
86.
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
87.
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
88.
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
89.
Chronic administration to rats of mood-stabilizers that are effective against mania in bipolar disorder, is reported to downregulate
markers of the brain arachidonic acid cascade. We hypothesized that chronic administration of lamotrigine, which is used to
treat depression and rapid cycling in bipolar disorder, might do so as well. Male CDF rats were administered a therapeutically
relevant dose of lamotrigine (10 mg/kg) or vehicle intragastrically once daily for 42 days. Protein levels of isoforms of
phospholipase A2 (PLA2) and of cyclooxygenase (COX), and the mRNA level of COX-2, were quantified in the frontal cortex using immunoblotting and
RT-PCR, respectively. Compared to vehicle-treated rats, chronic lamotrigine significantly decreased frontal cortex protein
and mRNA levels of COX-2 without altering protein levels of the PLA2 isoforms. Consistent with the hypothesis, lamotrigine and other mood-stabilizers have a common downregulatory action on COX-2
expression in rat brain, which may account in part for their efficacy in bipolar disorder. 相似文献
90.
No studies on the concentration dependency of the inhibition of Streptococcus mutans with xylitol are available. We studied xylitol-induced growth inhibition of two type strains, S. mutans NCTC 10449 and Ingbritt, and three clinical isolates of S. mutans. The strains were grown in Brain Hearth Infusion Medium in the presence of 0.001% (0.066 mM), 0.005% (0.33 mM), 0.01% (0.66
mM), 0.1% (6.6 mM), and 1% (66 mM) xylitol. Growth was followed by measuring the absorbance at a wavelength of 660 nm. The
highest xylitol concentration tested in this study, 1%, showed mean inhibition percentages ranging from 61% to 76% when the
growth inhibition of the five strains was compared to the control without xylitol at log-phase. For 0.1% xylitol, the inhibition
percentages ranged from 22% to 59%. A concentration dependency was seen in the growth inhibition, with 0.01% xylitol being
the lowest xylitol concentration inhibiting all five strains significantly (p < 0.001). The growth inhibition percentages determined for 0.01% xylitol, however, were low, and the inhibition was significantly
weaker as compared to 0.1% and 1% xylitol. Our results suggest that low xylitol concentrations of 0.1% (6.6 mM) could inhibit
mutans streptococci in vivo but even lower xylitol concentrations may be inhibitory. 相似文献