全文获取类型
收费全文 | 1372篇 |
免费 | 130篇 |
国内免费 | 36篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 39篇 |
2021年 | 49篇 |
2020年 | 33篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 38篇 |
2016年 | 32篇 |
2015年 | 34篇 |
2014年 | 88篇 |
2013年 | 84篇 |
2012年 | 50篇 |
2011年 | 63篇 |
2010年 | 49篇 |
2009年 | 63篇 |
2008年 | 79篇 |
2007年 | 81篇 |
2006年 | 71篇 |
2005年 | 59篇 |
2004年 | 52篇 |
2003年 | 42篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 17篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 29篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1972年 | 2篇 |
排序方式: 共有1538条查询结果,搜索用时 46 毫秒
961.
目的:研究稀土磁治疗床对食管癌、肺癌手术患者术后机体免疫力及切口疼痛的影响。方法:选食管癌患者37例,肺癌23例,采集手术前及稀土磁治疗床治疗后患者静脉血,检测T细胞亚群CD3 、CD4 、CD8 、CD4 /CD8 比值和NK细胞的比例变化,检查手术切口疼痛的恢复情况。结果:术后给予稀土磁治疗床治疗后与手术前相比较CD3 、CD4 、NK、CD4 /CD8 细胞有显著提高(P<0.05),也高于对照组术后的T细胞亚群水平(P<0.05)。结论:稀土磁治疗床可提高食管癌、肺癌患者术后的机体免疫力,减轻疼痛,有利于患者术后恢复。 相似文献
962.
963.
Plant succession and rhizosphere microbial communities in a recently deglaciated alpine terrain 总被引:4,自引:0,他引:4
Dagmar Tscherko Ute Hammesfahr Georg Zeltner Ellen Kandeler Reinhard Bcker 《Basic and Applied Ecology》2005,6(4):367-383
This study describes how early and late successional plant species affect soil microorganisms in alpine ecosystems. We quantify the relative importance of plant species and soil properties as determinants of belowground microbial communities. Sixteen plant species were selected from six successional stages (4–14–20–43–75–135 years) within the foreland of the Rotmoosferner glacier, Austria, and at one (reference) site outside the foreland. The size, composition and function of the communities of microorganism in the bulk soil and the rhizosphere were characterized by ninhydrin-reactive nitrogen, phospholipid fatty acids and enzyme activities (β-glucosidase, β-xylosidase, N-acetyl-β-glucosaminidase, leucine aminopeptidase, acid phosphatase, sulphatase). The results show that the microbial data could be grouped according to early (up to 43 years) and late-colonizing plant species (75 or more years). In early succession, no plant species or soil age effect was detected on the microbial biomass, phospholipid fatty acids, or enzyme activity. The rhizosphere microbial community was similar to that in the bulk soil, which in turn was determined by the abiotic environmental conditions. In late succession, improved soil conditions probably mediated plant species effects on the belowground microbial community. The most pronounced rhizosphere effects were attributed to plant species of the 75- and 135-year-old sites. The microbial colonization (size, composition, activity) of the bulk soil predominantly followed changes in vegetation cover, plant life forms and soil organic matter. In summary, the observed successional pattern of the above- and belowground communities provides an example of the facilitation models of primary succession. 相似文献
964.
965.
966.
Genomics efforts of the past decade have resulted in the identification of numerous genes with putative roles in disease processes, including tumor angiogenesis. To functionally validate these genes, cultured endothelial cells are indispensable tools, though these may not completely mimic the phenotype of tissue endothelial cells as the proper microenvironment is lacking. To obtain experimental data representative of normal physiology, the use of primary endothelial cells is preferred. However, these cells are usually limited in passage number, can be difficult to obtain and show great interindividual variety. Furthermore, transfection efficiency is very limited in primary cells, hampering applications in functional genomics and gene function analysis. The use of properly characterized alternative endothelial cell sources is therefore warranted. Here, we compared immortalized endothelial cells - HMEC, RF24 and EVLC2 - with primary HUVEC. We show that RF24, and to a slightly lesser extent HMEC, resembles primary HUVEC most on all facets examined. RF24, in contrast to EVLC2, express the endothelial markers CD31, CD34, CD105, vWF and VE-cadherin, and are capable of migration and tube formation in vitro. Furthermore, the expression levels of angiogenic growth factors and their receptors are comparable to that of primary EC. In addition, whereas primary HUVEC are resistant to transfection using common lipophilic transfection reagents, HMEC and RF24 could be readily transfected. Hence, these cells pose a valuable tool for functional genomics in angiogenesis research. 相似文献
967.
We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary
production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m < < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and
deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values.
Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO3
−–N + NH4
+–N) were consistently below the detection limit (0.05 μmol l−1) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l−1), total-P (0.29 μmol l−1), and total-N (33 μmol l−1), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos,
GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l−1 and 0.7–3.8 μmol C l−1 day−1. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m−2 and 3.2–5.8 mmol C m−2 day−1. Average values of epipelic chl a ranged from 131 to 549 mg m−2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average
epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m−2 day−1) than in intermediate and deep lakes (3.4 and 2.4 mmol C m−2 day−1). Total primary production (6.7–15.4 mmol C m−2 day−1) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables
were significantly higher in shallow lakes than in intermediate or deep lakes.
Handling editor: L. Naselli-Flores 相似文献
968.
This paper reports for the first time, the Primary cell culture of hepatopancreas from edible crab Scylla serrata using crab saline, L-15 (Leibovitz), 1 × L-15 + crab saline, 2 × L-15 + crab saline, 3 × L-15 and citrate buffer without
any serum. We could isolate and maintain E (Embryonalzellen), F (Fibrenzellen), B (Blasenzellen), R (Restzellen) and G (Granular
cells). Upon seeding the hepatopancreatic E, F, B, and R cells showed different survival pattern over time than granular cells.
A modified L-15 (3×) medium supported the best survival of hepatopancreatic E, F B, and R cells in in-vitro culture. However
granular cells could be maintained for 184 days with L-15 (1×) + crab saline. Fetal bovine serum was not effective additive
and hampered cell viability in present study. 相似文献
969.
Jia Dong Carl-Fredrik Mandenius Marc Lübberstedt Thomas Urbaniak Andreas K. N. Nüssler Daniel Knobeloch Jörg C. Gerlach Katrin Zeilinger 《Cytotechnology》2008,57(3):251-261
Optimization of cell culture media based on statistical experimental design methodology is a widely used approach for improving
cultivation conditions. We applied this methodology to refine the composition of an established culture medium for growth
of a human hepatoma cell line, C3A. A selection of growth factors and nutrient supplements were systematically screened according
to standard design of experiments (DoE) procedures. The results of the screening indicated that the medium additives hepatocyte
growth factor, oncostatin M, and fibroblast growth factor 4 significantly influenced the metabolic activities of the C3A cell
line. Surface response methodology revealed that the optimum levels for these factors were 30 ng/ml for hepatocyte growth
factor and 35 ng/ml for oncostatin M. Additional experiments on primary human hepatocyte cultures showed high variance in
metabolic activities between cells from different individuals, making determination of optimal levels of factors more difficult.
Still, it was possible to conclude that hepatocyte growth factor, epidermal growth factor, and oncostatin M had decisive effects
on the metabolic functions of primary human hepatocytes. 相似文献
970.
Polygonum viviparum is one of the first ectomycorrhizal (EM) plant species colonising primary successional sites at the Rotmoos glacier forefront
(Tyrolean Alps, Austria). On a site with soil development of about 150 years (2,400 m above sea level), mycobionts of P. viviparum were identified by morphotyping and fungal ribosomal deoxyribonucleic acid internal transcribed spacer sequencing. For studying
seasonal dynamics and spatial heterogeneity, ectomycorrhizae were sampled on five plots during all seasons. P. viviparum root tips were always EM. In total, 18 mycobiont taxa of the following genera were identified: Cenococcum (1), Cortinarius (2), Helvella (1), Inocybe (3), Russula (1), Sebacina (2), Thelephora (2) and Tomentella (6). All were non-specific EM partners of EM plants. As early as 2 weeks after spring snow melt, EM were well developed,
vital and showed high mycobiont diversity. The relative abundance of senescent root tips was lowest in spring and increased
throughout the year, with a maximum in winter (frozen soil). Thus, mycobiont growth and physiological activity obviously start
when soil is still under snow cover: We speculate that water availability is one important initiation factor for mycorrhizal
development under snow cover, when temperatures still range around the freezing point. Irrespectively of the season, most
abundant mycobionts at this primary successional site belonged to the genera Tomentella, Sebacina and Cenococcum, also in frozen soil. Spatial heterogeneity was high when considering species composition and diversity indices. Overall
mycobionts species richness was restricted at this site, probably because of the limited availability of fungal partners.
We regard the presence/absence of fungal partner and limiting abiotic impacts of the environment as key factors for the symbiotic
status of P. viviparum.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献