全文获取类型
收费全文 | 129423篇 |
免费 | 2740篇 |
国内免费 | 899篇 |
专业分类
133062篇 |
出版年
2023年 | 225篇 |
2022年 | 521篇 |
2021年 | 908篇 |
2020年 | 521篇 |
2019年 | 675篇 |
2018年 | 12527篇 |
2017年 | 11195篇 |
2016年 | 8612篇 |
2015年 | 2560篇 |
2014年 | 2405篇 |
2013年 | 3207篇 |
2012年 | 7464篇 |
2011年 | 15694篇 |
2010年 | 13711篇 |
2009年 | 9736篇 |
2008年 | 11924篇 |
2007年 | 13428篇 |
2006年 | 2294篇 |
2005年 | 2341篇 |
2004年 | 2680篇 |
2003年 | 2674篇 |
2002年 | 2273篇 |
2001年 | 555篇 |
2000年 | 368篇 |
1999年 | 323篇 |
1998年 | 385篇 |
1997年 | 274篇 |
1996年 | 262篇 |
1995年 | 230篇 |
1994年 | 230篇 |
1993年 | 248篇 |
1992年 | 156篇 |
1991年 | 180篇 |
1990年 | 154篇 |
1989年 | 116篇 |
1988年 | 118篇 |
1987年 | 103篇 |
1986年 | 70篇 |
1985年 | 95篇 |
1984年 | 103篇 |
1983年 | 88篇 |
1982年 | 85篇 |
1981年 | 80篇 |
1980年 | 81篇 |
1979年 | 73篇 |
1977年 | 50篇 |
1975年 | 43篇 |
1973年 | 42篇 |
1972年 | 277篇 |
1971年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
Terje D Josefsen Karen K Sørensen Torill Mørk Svein D Mathiesen Kathrine A Ryeng 《Acta veterinaria Scandinavica》2007,49(1):27
Background
In a project to determine the causes of winter mortality in reindeer in Finnmark County, northern Norway, the most frequent diagnosis turned out to be complete emaciation, despite several of the reindeer having been given silage for up to 4 weeks before they died. The present paper describes autopsy results and other findings in these animals. 相似文献943.
Amar S Ecke W Becker HC Möllers C 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2008,116(8):1051-1061
Improving oil and protein quality for food and feed purposes is an important goal in rapeseed (Brassica napus L.) breeding programs. Rapeseed contains phytosterols, used to enrich food products, and sinapate esters, which are limiting
the utilization of rapeseed proteins in the feed industry. Increasing the phytosterol content of oil and lowering sinapate
ester content of meal could increase the value of the oilseed rape crop. The objective of the present study was to identify
quantitative trait loci (QTL) for phytosterol and sinapate ester content in a winter rapeseed population of 148 doubled haploid
lines, previously found to have a large variation for these two traits. This population also segregated for the two erucic
acid genes. A close negative correlation was found between erucic acid and phytosterol content (Spearman’s rank correlation,
r
s = −0.80**). For total phytosterol content, three QTL were detected, explaining 60% of the genetic variance. The two QTL with the strongest
additive effects were mapped on linkage groups N8 and N13 within the confidence intervals of the two erucic acid genes. For
sinapate ester content four QTL were detected, explaining 53% of the genetic variance. Again, a close negative correlation
was found between erucic acid and sinapate ester content (r
s = −0.66**) and the QTL with the strongest additive effects mapped on linkage groups N8 and N13 within the confidence intervals of the
two erucic acid genes. The results suggests, that there is a pleiotropic effect of the two erucic acid genes on phytosterol
and sinapate ester content; the effect of the alleles for low erucic acid content is to increase phytosterol and sinapate
ester content. Possible reasons for this are discussed based on known biosynthetic pathways.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
944.
Airong Li Yue Zhu Xingbing He Xingjun Tian Liang Xu Wu Ni Ping Jiang 《World journal of microbiology & biotechnology》2008,24(4):569-572
Six selected plants, belonging to 3 families from Nanjing of China, were extracted with the solvent 95% (v/v) ethanol to yield
11 extracts. The extracts were evaluated for their effects on the growth of eight clinical bacteria, two fungi and one yeast
using a modified agar diffusion method. The results showed that the majority of the extracts investigated showed greater activities
against the Gram-positive bacteria than against the Gram-negative bacteria, the fungi and the yeast. The strongest antimicrobial
activity was exhibited by the stem extracts of Mahonia fortunei against multiresistant Staphylococcus aureus strains, followed by the stem extracts of Mahonia bealei, while Bacillus thuringiensis was the most sensitive to all extracts. 相似文献
945.
Irina Vaseva Dessislava Todorova Jiří Malbeck Alena Trávníčková Ivana Macháčková 《Acta Physiologiae Plantarum》2008,30(2):151-155
Changes in cytokinin pool and cytokinin oxidase/dehydrogenase activity (CKX EC: 1.5.99.12) in response to increasing abscisic
acid (ABA) concentrations (0.5–10 μM) were assessed in the last fully expanded leaves and secondary roots of two pea (Pisum sativum) varieties with different vegetation periods. Certain organ diversity in CKX response to exogenous ABA was observed. Treatment
provoked altered cytokinin pool in the aboveground parts of both studied cultivars. Specific CKX activity was influenced significantly
basically in roots of the treated plants. Results suggest that ABA-mediated cytokinin pool changes are leaf-specific and involve
certain root signals in which CKX activity presents an important link. This enzymatic activity most probably regulates vascular
transport of active cytokinins from roots to shoots. 相似文献
946.
Human leptin induces angiogenesis in vivo 总被引:1,自引:0,他引:1
Anagnostoulis S Karayiannakis AJ Lambropoulou M Efthimiadou A Polychronidis A Simopoulos C 《Cytokine》2008,42(3):353-357
Leptin is an adipocyte-produced peptide, which plays a crucial role in the regulation of body weight. There is also evidence that leptin stimulates endothelial cell proliferation and the formation of capillary-like tubes in vitro. The disc angiogenesis system was used to measure the angiogenic effect of leptin in vivo. Discs containing 25, 50, 100 and 250 ng/ml of leptin were implanted subcutaneously in Wistar rats, removed after a growth period of 7 and 14 days, and compared with spontaneous growth controls and with positive controls containing equivalent doses of vascular endothelial growth factor (VEGF). Discs were examined morphologically for stroma and vessel development and by immunohistochemistry for quantitative evaluation of angiogenesis. The specificity of the angiogenic effect of leptin was tested by blocking leptin with a polyclonal anti-leptin antibody. Leptin induced a significant level of angiogenesis in a dose-dependent manner both at 7 and 14 days, with a peak at the dose of 100 ng/ml. The angiogenic activity of leptin was completely abolished by the anti-leptin neutralizing antibody. VEGF also induced significant dose-dependent angiogenesis at the same time points with a peak observed at a concentration of 100 ng/ml. The angiogenic response to leptin was significantly higher at 7 days compared with VEGF but not at the 14-day time point. In conclusion, leptin has a specific angiogenic effect in vivo, which is dose- and time-dependent in a concentration range of 25–250 ng/ml. This effect is equivalent to the angiogenic effect of VEGF but is evident earlier compared with VEGF. 相似文献
947.
Yurixhi Maldonado–López Edelmira Linares–Mazari Robert Bye Guillermo Delgado Francisco J. Espinosa–García 《Economic botany》2008,62(2):161-170
Mexican Arnica Anti–Inflammatory Action: Plant Age Is Correlated with the Concentration of Anti–inflammatory Sesquiterpenes
in the Medicinal Plant
Heterotheca inuloides
Cass. (Asteraceae). Mexican árnica (Heterotheca inuloides Cass.) is a widely used anti–inflammatory medicinal plant in Mexican folk medicine. Although it has been suggested that plant
age, fertilization, and harvesting regime influence the concentration of secondary compounds affecting the therapeutic activity
of the plant, the effect of these variables on the concentration of the Mexican árnica anti–inflammatory compounds was not
known. We quantified anti–inflammatory sesquiterpenes (caryolan–1, 9β–diol, cadalen–15–oic acid, 7–hydroxycadalene, 4–hydroxy–2–isopropyl–4,
7–dimethyl–1[4H] naftalinone, 7–hydroxy–4αH–3, 4–dihydrocadalene, β–caryophyllene, and β–caryophyllene epoxide) in Mexican
árnica plants subjected to fertilization and successive harvests of flowering stems, conditions that mimic the cultivation
and harvesting for árnica in México. Fertilization and successive harvesting and their interaction had no significant effect
on the concentration of anti–inflammatory compounds. However, the concentrations of these compounds were 60% higher in flowering
stems from 15–month–old plants than in those from 4– or 8–month–old plants and was independent of the number of harvests and
fertilization regime applied. 相似文献
948.
Raşit Urhan 《Biologia》2008,63(3):395-401
Two new species of zerconid mites, Zercon uludagicus sp. n. and Z. huseyini sp. n., from Turkey are described and illustrated. The similarities and differences between the species are discussed. The
lists of the taxonomic diagnostic key to adults of Zercon species known from Turkey are also given. 相似文献
949.
950.
Amornrat Chumthong Mana Kanjanamaneesathian Ashara Pengnoo Ruedeekorn Wiwattanapatapee 《World journal of microbiology & biotechnology》2008,24(11):2499-2507
Endospores of B. megaterium were formulated in granule formulations with sodium alginate, lactose and polyvinylpyrrolidone (PVP K-30) by the wet granulation
technique. The granule formulation exhibited good physical characteristics, such as high-water solubility and optimal viscosity,
that would be suitable for spray application. The bacteria remained viable in the dry granule formulation at 109 c.f.u./g after 24 months storage at room temperature. Under laboratory conditions, aqueous solutions of the formulation showed
high activity against mycelial growth of R. solani (99.64 ± 0.14% mycelial inhibition). High viability of the bacterial antagonist on leaf sheath and leaf blade at day 7 after
spraying with the formulation was observed (approximately 106 c.f.u./g of plant). Application of an equivalent number of un-formulated endospores resulted in much loss of the bacterial
endospores even 1 day after application. In a small pilot field study, an aqueous solution of the formulation (3%w/v) applied
by spraying at days 1, 5 and 10 after pathogen inoculation of the rice plants was more effective in suppressing rice sheath
blight disease than one application of a fungicide (Iprodione) at day 1. Additionally, rice plants sprayed with the aqueous
solution of the granule formulation had higher panicle and whole kernel weights than those of fungicide-treated and control
(untreated) plants. 相似文献