首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1452篇
  免费   68篇
  2023年   11篇
  2022年   23篇
  2021年   41篇
  2020年   18篇
  2019年   24篇
  2018年   29篇
  2017年   33篇
  2016年   40篇
  2015年   58篇
  2014年   55篇
  2013年   92篇
  2012年   112篇
  2011年   119篇
  2010年   69篇
  2009年   72篇
  2008年   90篇
  2007年   69篇
  2006年   63篇
  2005年   53篇
  2004年   49篇
  2003年   50篇
  2002年   50篇
  2001年   36篇
  2000年   38篇
  1999年   36篇
  1998年   7篇
  1997年   6篇
  1996年   6篇
  1995年   5篇
  1994年   4篇
  1993年   10篇
  1992年   13篇
  1991年   13篇
  1990年   18篇
  1989年   17篇
  1988年   10篇
  1987年   13篇
  1986年   10篇
  1985年   5篇
  1983年   9篇
  1982年   4篇
  1979年   6篇
  1978年   3篇
  1977年   6篇
  1976年   2篇
  1975年   4篇
  1973年   3篇
  1972年   4篇
  1970年   2篇
  1968年   2篇
排序方式: 共有1520条查询结果,搜索用时 15 毫秒
31.
32.
Toxoplasma gondii was found in tissues of a six-year-old female Pallas cat (Felis manul) from the Milwaukee County Zoo. Toxoplasma gondii meronts (types D and E), gamonts, and oocysts were present in the epithelium of the small intestine. Numerous unsporulated oocysts were present in the intestinal lumen. The cat died of acute, overwhelming toxoplasmosis. Necrotic enteritis, multifocal necrotizing granulomatous hepatitis, and pneumonia were the prominent lesions.  相似文献   
33.
34.
One day old chicks of Japanese quail were exposed to different photoperiods (LD, 8:16, 13.5:10.5, 16:8 and LL) and observations (testes weight, cloacal gland size, body weight and circulating thyroxine and triiodothyronine) were taken at the age of 3, 5, 7, 9 and 16 weeks. Results indicate that immediate reproductive development occurred in birds exposed to long photoperiods (greater than 12 hr). Growth under LD 8:16, was not apparent till 7th week and by 16 weeks, degree of gonadal development was similar in all the birds, irrespective of photoperiodic treatment. Whereas body weight of the intermediate and long day (LD 13.5:10.5, 16:8 and LL) treated birds increased upto 5th week and remained constant thereafter. But the chicks maintained under short day length (LD 8:16), showed spontaneous increase till the end of the study and birds were much heavier compared to all other groups. Plasma T4 concentration increased with increasing age till 9th week and remained unaltered thereafter. On the other hand T3 level did not change till 7th week followed by a decline. It is suggested that the initiation and degree of gonadal growth in quail depends on the availability of daily photoperiod, until the achievement of full breeding condition. Peak level of T4 observed in 9 week old birds may be involved in the development of photorefractoriness at that age.  相似文献   
35.
In the present study the potentials of aqueous extracts of the two plants, neem (Azadirachta indica) and Tulsi (Ocimum sanctum) were examined in alleviating arsenic toxicity in rice (Oryza sativa L.) plants grown in hydroponics. Seedlings of rice grown for 8 days in nutrient solution containing 50 μM sodium arsenite showed decline in growth, reduced biomass, altered membrane permeability and increased production of superoxide anion (O2·−), H2O2 and hydroxyl radicals (·OH). Increased lipid peroxidation marked by elevated TBARS (thiobarbituric acid reactive substances) level, increased protein carbonylation, alterated levels of ascorbate, glutathione and increased activities of enzymes SOD (superoxide dismutase), CAT (catalase), APX (ascorbate peroxidase) and GPX (glutathione peroxidase) were noted in the seedlings on As treatment. Exogenously added leaf aqueous extracts of Azadirachta indica (0.75 mg mL−1, w/v) and Ocimum sanctum (0.87 mg mL−1, w/v) in the growth medium considerably alleviated As toxicity effects in the seedlings, marked by reduced As uptake, restoration of membrane integrity, reduced production of ROS, lowering oxidative damage and restoring the levels of ascorbate, glutathione and activity levels of antioxidative enzymes. Arsenic uptake in the seedlings declined by 72.5% in roots and 72.8% in shoots, when A. indica extract was present in the As treatment medium whereas with O. sanctum extract, the uptake declined by 67.2% in roots and 70.01% in shoots. Results suggest that both A. indica and O. sanctum aqueous extracts have potentials to alleviate arsenic toxicity in rice plants and that A. indica can serve as better As toxicity alleviator compared to O. sanctum.  相似文献   
36.
37.
38.
In this study, attempts have been made to identify and characterize water buffalo (Bubalus bubalis) mammary derived growth inhibitor (MDGI) gene, isolated from a mammary gland cDNA library of lactating buffalo. The complete MDGI cDNA was of 698 nucleotides, consisting 61 nucleotides in 5′ UTR, coding region of 402 nucleotides, and 235 nucleotides representing the 3′ UTR. Comparison of nucleotide and deduced amino acid sequence data with that of MDGI//fatty acid binding protein (FABP) of other species shows three buffalo specific nucleotide changes while seven nucleotide changes were common to cattle and buffalo. Buffalo and cattle MDGI had 100% amino acid sequence similarity, which also shared three amino acid changes: 34 (Ala-Gly), 109 (Leu-Met), and 132 (Glu-Gln) as compared to other species. Comparison with FABPs reported from other cattle tissues revealed highest amino acid sequence similarity with FABP-heart (100%) and least with FABP-liver (20.5%). Phylogenetic analysis revealed cattle MDGI to be closest to buffalo, while mouse MDGI was distantly placed, whereas different tissue derived FABPs of cattle showed FABP-heart closest and FABP-epidermis most distantly placed from buffalo MDGI. This report also differs from the earlier findings that MDGI is intermediate of FABP-heart and adipose.  相似文献   
39.
The present study aims to understand the existing genetic diversity and structure of six native cattle breeds (Rathi, Tharparkar, Nagori, Mewati, Gir, and Kankrej) adapted to the north-western arid and semi-arid region of India based on microsatellite loci. Various diversity estimates, mean number of alleles (12.84); effective number of alleles (5.02); gene diversity (0.769), and observed heterozygosity (0.667) reflected the existence of substantial within-breed diversity in all the investigated cattle breeds. Mean estimates of F-statistics: FIT = 0.144 ± 0.023, FIS = 0.071 ± 0.021, and FST = 0.078 ± 0.014 were significantly different from zero (P < 0.05). The interbreed relationships indicated moderate level of breed differentiation between the six cattle breeds with least differentiation between Kankrej-Mewati pair. The phylogeny structuring further supported close grouping of Kankrej and Mewati breeds. Correspondence analysis plotted Rathi, Tharparkar, and Gir individuals into three separate areas of multivariate space; whereas, Kankrej, Mewati, and Nagori cattle showed low breed specific clustering. This reflected the existence of discrete genetic structure for Tharparkar, Rathi, and Gir, the prominent dairy breeds of the region; whereas, admixture was observed for Kankrej, Mewati, and Nagori individuals.  相似文献   
40.
A new series of functionalized amino acid derivatives N-substituted 1-N-(tert-butoxycarbonyl)-2,2-dimethyl-4-phenyl-5-oxazolidine carboxamide (1-17) and 1-N-substituted-3-amino-2-hydroxy-3-phenylpropane-1-carboxamide (18-34) were synthesized and evaluated for their in vitro cytotoxicity against human cancer cell lines. Compound 6 has shown interesting cytotoxicity (IC50 = 5.67 μm) in ovarian cancer, while compound 10 exhibited promising cytotoxicity in ovarian (IC50 = 6.1 μm) and oral (IC50 = 4.17 μm) cancers. These compounds could be of use in designing new anti-cancer agents.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号