全文获取类型
收费全文 | 5696篇 |
免费 | 726篇 |
国内免费 | 3篇 |
专业分类
6425篇 |
出版年
2022年 | 38篇 |
2021年 | 88篇 |
2020年 | 40篇 |
2019年 | 50篇 |
2018年 | 62篇 |
2017年 | 52篇 |
2016年 | 99篇 |
2015年 | 170篇 |
2014年 | 189篇 |
2013年 | 231篇 |
2012年 | 281篇 |
2011年 | 295篇 |
2010年 | 156篇 |
2009年 | 137篇 |
2008年 | 266篇 |
2007年 | 256篇 |
2006年 | 244篇 |
2005年 | 244篇 |
2004年 | 211篇 |
2003年 | 196篇 |
2002年 | 188篇 |
2001年 | 204篇 |
2000年 | 212篇 |
1999年 | 156篇 |
1998年 | 76篇 |
1997年 | 74篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 74篇 |
1993年 | 78篇 |
1992年 | 149篇 |
1991年 | 134篇 |
1990年 | 129篇 |
1989年 | 113篇 |
1988年 | 107篇 |
1987年 | 122篇 |
1986年 | 99篇 |
1985年 | 101篇 |
1984年 | 96篇 |
1983年 | 71篇 |
1982年 | 63篇 |
1981年 | 66篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 51篇 |
1977年 | 44篇 |
1976年 | 46篇 |
1975年 | 39篇 |
1974年 | 43篇 |
1973年 | 58篇 |
排序方式: 共有6425条查询结果,搜索用时 15 毫秒
121.
122.
During early pregnancy in the rat, focal adhesions disassemble in uterine luminal epithelial cells at the time of implantation
to facilitate their removal so that the implanting blastocyst can invade into the underlying endometrial decidual cells. This
study investigated the effect of ovarian hormones on the distribution and protein expression of two focal adhesion proteins,
talin and paxillin, in rat uterine luminal and glandular epithelial cells under various hormone regimes. Talin and paxillin
showed a major distributional change between different hormone regimes. Talin and paxillin were highly concentrated along
the basal cell surface of uterine luminal epithelial cells in response to oestrogen treatment. However, this prominent staining
of talin and paxillin was absent and also a corresponding reduction of paxillin expression was demonstrated in response to
progesterone alone or progesterone in combination with oestrogen, which is also observed at the time of implantation. In contrast,
the distribution of talin and paxillin in uterine glandular epithelial cells was localised on the basal cell surface and remained
unchanged in all hormone regimes. Thus, not all focal adhesions are hormonally dependent in the rat uterus; however, the dynamics
of focal adhesion in uterine luminal epithelial cells is tightly regulated by ovarian hormones. In particular, focal adhesion
disassembly in uterine luminal epithelial cells, a key component to establish successful implantation, is predominantly under
the influence of progesterone. 相似文献
123.
Catherine Murphy Sarah Hotchkiss Jenny Worthington Stephanie R. McKeown 《Journal of applied phycology》2014,26(5):2211-2264
This review discusses studies on marine macroalgae that have been investigated for their potential as sources of novel anti-cancer drugs. The review highlights the very large number of studies of crude, partially purified and purified seaweed extracts, collected from many locations, which have shown potential as sources of potent anti-cancer drugs when tested in vitro and/or in vivo. The activity of polysaccharides, polyphenols, proteinaceous molecules, carotenoids, alkaloids, terpenes and others is described here. In some reports, mechanistic studies have identified specific inhibitory activity on a number of key cellular processes including apoptosis pathways, telomerase and tumour angiogenesis. However, despite the potential shown by these studies, translation to clinically useful preparations is almost non-existent. It is hoped this review will serve as a source document and guide for those carrying out research into the potential use of macroalgae as a source of novel anti-cancer agents. 相似文献
124.
Although leaf size is one of the most responsive plant traits to environmental change, the functional benefits of large versus small leaves remain unclear. We hypothesized that modification of leaf size within species resulting from differences in irradiance can allow leaves to acclimate to different photosynthetic or evaporative conditions while maintaining an efficient balance between hydraulic supply (vein density) and evaporative demand. To test this, we compared the function and anatomy of leaf hydraulic systems in the leaves of a woody angiosperm (Toona ciliata M. Roem.) grown under high and low irradiance in controlled conditions. Our results confirm that in this species, differential leaf expansion regulates the density of veins and stomata such that leaf hydraulic conductance and stomatal conductance remain proportional. A broader sample of field-grown tree species suggested that differences in leaf venation and stomatal traits induced by sun and shade were not regulated by leaf size in all cases. Our results, however, suggest that leaf size plasticity can provide an efficient way for plants to acclimate hydraulic and stomatal conductances to the contrasting evaporative conditions of sun and shade. 相似文献
125.
Objective
To assess the clinical effect of medication monitoring using the West Wales Adverse Drug Reaction (ADR) Profile for Respiratory Medicine.Design
Single-site parallel-arm pragmatic trial using stratified randomisation.Setting
Nurse-led respiratory outpatient clinic in general hospital in South Wales.Participants
54 patients with chronic respiratory disease receiving bronchodilators, corticosteroids or leukotriene receptor antagonists.Intervention
Following initial observation of usual nursing care, we allocated participants at random to receive at follow up: either the West Wales ADR Profile for Respiratory Medicine in addition to usual care (‘intervention arm’ with 26 participants); or usual care alone (‘control arm’ with 28 participants).Main Outcome Measures
Problems reported and actions taken.Results
We followed up all randomised participants, and analysed data in accordance with treatment allocated. The increase in numbers of problems per participant identified at follow up was significantly higher in the intervention arm, where the median increase was 20.5 [inter-quartile range (IQR) 13–26], while that in the control arm was −1 [−3 to +2] [Mann-Whitney U test: z = 6.28, p<0.001]. The increase in numbers of actions per participant taken at follow up was also significantly higher in the intervention arm, where the median increase was 2.5 [1]–[4] while that in the control arm was 0 [−1.75 to +1] [Mann-Whitney U test: z = 4.40, p<0.001].Conclusion
When added to usual nursing care, the West Wales ADR Profile identified more problems and prompted more nursing actions. Our ADR Profile warrants further investigation as a strategy to optimise medication management.Trial Registration
Controlled-trials.com ISRCTN10386209 相似文献126.
The prediction of adult emergence times in insect populations can be greatly complicated by microclimatic gradients, especially in circumstances where distributions of juveniles along those gradients vary from year to year. To investigate adult emergence patterns in topographically heterogeneous habitats, we built a model of postdiapause development of the Bay checkerspot butterfly, Euphydryas editha bayensis. The model uses slope-specific insolation as the rate-controlling variable, and accounts for both solar exposure of the habitat and cloud cover. Instar-specific larval mass gains per unit of insolation were determined from mark-recapture experiments. A small correction for daily low temperatures was used to calibrate the model to five years of field data on larval mass. The model predicted mean mass of 90% of larval samples within 4 clear days over a 70–120 day growing season. The magnitude of spatial variation in emergence times across habitat slopes is greater than annual variation in emergence times due to yearly weather conditions. Historical variation (yearly shifts in larval distributions across slopes) is an important determinant of mean population emergence dates. All of these factors need to be considered in understanding adult emergence phenology in this butterfly and in other insects inhabiting heterogeneous thermal environments. Such an understanding can be useful in managing insect populations for both pest control and conservation. 相似文献
127.
Production of nuclear transfer-derived swine that express the enhanced green fluorescent protein. 总被引:22,自引:0,他引:22
K W Park H T Cheong L Lai G S Im B Kühholzer A Bonk M Samuel A Rieke B N Day C N Murphy D B Carter R S Prather 《Animal biotechnology》2001,12(2):173-181
The ability to add or delete specific genes in swine will likely provide considerable benefits not just to agriculture but also to medicine, where pigs have potential as models for human disease and as organ donors. Here we have transferred nuclei from a genetically modified fibroblast cell line to porcine oocytes, matured in vitro under defined culture conditions, to create piglets expressing enhanced green fluorescent protein. The nuclear transfer-derived piglets were of normal size, although some mild symptoms of "large offspring syndrome" were evident. These experiments represent a next step towards creating swine with more useful genetic modifications. 相似文献
128.
The properties of transketolase from photosynthetic tissue 总被引:1,自引:0,他引:1
Transketolase (E.C. 2.2.1.1.) has been partially purified from wheat (Triticum aestivum, cv. Sappo) and spinach (Spinacia oleracea) leaves. The fully-active enzyme is a tetramer of relative molecular mass (Mr) of 150 kMr requiring thiamin pyrophosphate for maximal activity, and dissociating into a 74 kMr dimer in its absence or in dilute solution. The chloroplastic transketolase (over 75% of the cellular total) is magnesium-stimulated but the cytosolic form is magnesium-insensitive. Both chloroplastic and cytosolic transketolase showed similar broad specificities towards several ketose phosphate substrates including fructose 6-phosphate and sedoheptulose 7-phosphate. Wheat and spinach leaf transketolases are not light-activated and closely resemble the yeast enzyme in many of their properties.Abbreviations Mr
relative molecular mass
- TPP
thiamin pyrophosphate
- Tris
2-amino-2-(hydroxymethyl)-1,3-propandiol 相似文献
129.
Oral Antibiotic Treatment of Mice Exacerbates the Disease Severity of Multiple Flavivirus Infections