全文获取类型
收费全文 | 1331篇 |
免费 | 106篇 |
国内免费 | 3篇 |
专业分类
1440篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 39篇 |
2021年 | 67篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 44篇 |
2017年 | 30篇 |
2016年 | 45篇 |
2015年 | 56篇 |
2014年 | 64篇 |
2013年 | 88篇 |
2012年 | 107篇 |
2011年 | 109篇 |
2010年 | 42篇 |
2009年 | 49篇 |
2008年 | 85篇 |
2007年 | 61篇 |
2006年 | 48篇 |
2005年 | 34篇 |
2004年 | 35篇 |
2003年 | 33篇 |
2002年 | 25篇 |
2001年 | 35篇 |
2000年 | 35篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 7篇 |
排序方式: 共有1440条查询结果,搜索用时 0 毫秒
71.
Qadri Q Sameer AS Shah ZA Hamid A Alam S Manzoor S Siddiqi MA 《Genetics and molecular research : GMR》2011,10(4):3038-3045
Glutathione-S-transferase P1 (GSTP1) is a critical enzyme of the phase II detoxification pathway. One of the common functional polymorphisms of GSTP1 is A→G at nucleotide 313, which results in an amino acid substitution (Ile105Val) at the substrate binding site of GSTP1 and reduces catalytic activity of GSTP1. To investigate the GSTP1 Ile105Val genotype frequency in prostate cancer cases in the Kashmiri population, we designed a case-control study, in which 50 prostate cancer cases and 45 benign prostate hyperplasia cases were studied for GSTP1 Ile105Val polymorphism, compared to 80 controls taken from the general population, employing the PCR-RFLP technique. We found the frequency of the three different genotypes of GSTP1 Ile105Val in our ethnic Kashmir population, i.e., Ile/Ile, Ile/Val and Val/Val, to be 52.4, 33.3 and 14.3% among prostate cancer cases, 48.5, 37.5 and 14% among benign prostate hyperplasia cases and 73.8, 21.3 and 5% in the control population, respectively. There was a significant association between the GSTP1 Ile/Val genotype and the advanced age group among the cases. We conclude that GSTP1 Ile/Val polymorphism is involved in the risk of prostate cancer development in our population. 相似文献
72.
A rigorous theoretical investigation has been performed on the propagation of cylindrical and spherical Gardner solitons (GSs) associated with dust-ion-acoustic (DIA) waves in a dusty plasma consisting of inertial ions, negatively charged immobile dust, and two populations of kappa distributed electrons having two distinct temperatures. The well-known reductive perturbation method has been used to derive the modified Gardner (mG) equation. The basic features (amplitude, width, polarity, etc.) of nonplanar DIA modified Gardner solitons (mGSs) have been thoroughly examined by the numerical analysis of the mG equation. It has been found that the characteristics of the nonplanar DIA mGSs significantly differ from those of planar ones. It has been also observed that kappa distributed electrons with two distinct temperatures significantly modify the basic properties of the DIA solitary waves and that the plasma system under consideration supports both compressive and rarefactive DIA mGSs. The present investigation should play an important role for understanding localized electrostatic disturbances in space and laboratory dusty plasmas where stationary negatively charged dust, inertial ions, and superthermal electrons with two distinct temperatures are omnipresent ingredients. 相似文献
73.
Zlotorynski E Rahat A Skaug J Ben-Porat N Ozeri E Hershberg R Levi A Scherer SW Margalit H Kerem B 《Molecular and cellular biology》2003,23(20):7143-7151
Fragile sites are specific loci that form gaps, constrictions, and breaks on chromosomes exposed to partial replication stress and are rearranged in tumors. Fragile sites are classified as rare or common, depending on their induction and frequency within the population. The molecular basis of rare fragile sites is associated with expanded repeats capable of adopting unusual non-B DNA structures that can perturb DNA replication. The molecular basis of common fragile sites was unknown. Fragile sites from R-bands are enriched in flexible sequences relative to nonfragile regions from the same chromosomal bands. Here we cloned FRA7E, a common fragile site mapped to a G-band, and revealed a significant difference between its flexibility and that of nonfragile regions mapped to G-bands, similar to the pattern found in R-bands. Thus, in the entire genome, flexible sequences might play a role in the mechanism of fragility. The flexible sequences are composed of interrupted runs of AT-dinucleotides, which have the potential to form secondary structures and hence can affect replication. These sequences show similarity to the AT-rich minisatellite repeats that underlie the fragility of the rare fragile sites FRA16B and FRA10B. We further demonstrate that the normal alleles of FRA16B and FRA10B span the same genomic regions as the common fragile sites FRA16C and FRA10E. Our results suggest that a shared molecular basis, conferred by sequences with a potential to form secondary structures that can perturb replication, may underlie the fragility of rare fragile sites harboring AT-rich minisatellite repeats and aphidicolin-induced common fragile sites. 相似文献
74.
Isolation and screening of potential actinobacteria for rapid composting of rice straw 总被引:2,自引:0,他引:2
Rice straw is produced as a by-product from rice cultivation, which is composed largely of lignocellulosic materials amenable to general biodegradation. Lignocellulolytic actinobacteria can be used as a potential agent for rapid composting of bulky rice straw. Twenty-five actinobacteria isolates were isolated from various in situ and in vitro rice straw compost sources. Isolates A2, A4, A7, A9 and A24 were selected through enzymatic degradation of starch, cellulose and lignin followed by the screening for their adaptability on rice straw powder amended media. The best adapted isolate (A7) was identified as Micromonospora carbonacea. It was able to degrade cellulose, hemicelluloses and carbon significantly (P ≤ 0.05) over the control. C/N ratio was reduced to 18.1 from an initial value of 29.3 in 6 weeks of composting thus having the potential to be used in large scale composting of rice straw. 相似文献
75.
Population dynamics of M. triticoryzae in five rice-based cropping systems have revealed that rice was the main host. Most of the population growth which contributed to the peak population density in September occurred in the rice crop. The other crops in the Rabi and summer seasons had a profound influence on the height of the peak in the succeeding rice crop. Some level of reproduction occurred in wheat, greengram and berseem in Rabi which contributed to relatively higher equilibrium densities. The potato variety Pusa Bahar increased the population density while Pusa Badshah decreased it. The lower temperature during the Rabi season also limited the rate of population growth. The incorporation of organic matter into the soil, either as crop residues of greengram or berseem, reduced the population growth of M. triticoryzae . 相似文献
76.
77.
Christopher M. R. Bax Vijai S. Shankar A. S. M. Towhidul Alam Bridget E. Bax Baljit S. Moonga Christopher L. -H. Huang Mone Zaidi Barry R. Rifkin 《Bioscience reports》1993,13(3):169-174
We report the effects of tetracycline analogues on cytosolic Ca2+ transients resulting from application of ionic nickel (Ni2+), a potent surrogate agonist of the osteoclast Ca2+ receptor. Preincubation with minocycline (1 mg/l) or a chemically modified tetracycline, 4-dedimethyl-aminotetracycline (CMT-1) (1 or 10 mg/l), resulted in a significant attenuation of the magnitude of the cytosolic [Ca2+] response to an application of 5 mM-[Ni2+]. Preincubation with doxycycline (1 or 10 mg/l) failed to produce similar results. In addition, application of minocycline alone (0.1–100 mg/l) resulted in a 3.5-fold elevation of cytosolic [Ca2+]. The results suggest a novel action of tetracyclines on the osteoclast Ca2+ receptor. 相似文献
78.
Chemopreventive potential of H. indicus on 7,12-dimethyl-benz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoyl 13-phorbol acetate (TPA) promoted murine skin carcinogenesis has been assessed. Topical application of H. indicus resulted in significant protection against cutaneous tumorigenesis. Topical application of plant extract prior to that of TPA resulted in significant inhibition against TPA-caused induction of epidermal ornithine decarboxylase (ODC) activity and DNA synthesis. Application of H. indicus at a dose level of 1.5 and 3.0 mg/kg body weight in acetone prior to that of TPA treatment resulted in significant inhibition of oxidative stress. The level of lipid peroxidation was significantly reduced. In addition, depleted levels of glutathione and reduced activities of antioxidant enzymes were restored respectively). The results indicate that H. indicus is a potent chemopreventive agent in skin carcinogenesis. 相似文献
79.
Effect of the Environment on Genotypic Diversity of Actinomyces naeslundii and Streptococcus oralis in the Oral Biofilm 总被引:1,自引:0,他引:1 下载免费PDF全文
James S. Paddick Susan R. Brailsford Edwina A. M. Kidd Steven C. Gilbert Douglas T. Clark Sharmin Alam Zoe J. Killick David Beighton 《Applied microbiology》2003,69(11):6475-6480
The genotypic diversity of Actinomyces naeslundii genospecies 2 (424 isolates) and Streptococcus oralis (446 isolates) strains isolated from two sound approximal sites in all subjects who were either caries active (seven subjects) or caries free (seven subjects) was investigated by using the repetitive extragenic palindromic PCR. The plaque from the caries-active subjects harbored significantly greater proportions of mutans streptococci and lactobacilli and a smaller proportion of A. naeslundii organisms than the plaque sampled from the caries-free subjects. These data confirmed that the sites of the two groups of subjects were subjected to different environmental stresses, probably determined by the prevailing or fluctuating acidic pH values. We tested the hypothesis that the microfloras of the sites subjected to greater stresses (the plaque samples from the caries-active subjects) would exhibit reduced genotypic diversity since the sites would be less favorable. We found that the diversity of A. naeslundii strains did not change (χ2 = 0.68; P = 0.41) although the proportional representation of A. naeslundii was significantly reduced (P < 0.05). Conversely, the diversity of the S. oralis strains increased (χ2 = 11.71; P = 0.0006) and the proportional representation of S. oralis did not change. We propose that under these environmental conditions the diversity and number of niches within the oral biofilm that could be exploited by S. oralis increased, resulting in the increased genotypic diversity of this species. Apparently, A. naeslundii was not able to exploit the new niches since the prevailing conditions within the niches may have been deleterious and not supportive of its proliferation. These results suggest that environmental stress may modify a biofilm such that the diversity of the niches is increased and that these niches may be successfully exploited by some, but not necessarily all, members of the microbial community. 相似文献
80.
Li Wang Lin Li M. J. Alam Yuhuan Geng Zhiyong Li Shinji Yamasaki & Lei Shi 《FEMS microbiology letters》2008,282(1):15-21
The marine dinoflagellate genus Alexandrium includes a number of species that produce potent neurotoxins responsible for paralytic shellfish poisoning, which in humans may cause muscular paralysis, neurological symptoms and, in extreme cases, death. Because of the genetic diversity of different genera and species, molecular tools may help to detect the presence of target microorganisms in marine field samples. Here we employed a loop-mediated isothermal amplification (LAMP) method for the rapid and simple detection of toxic Alexandrium species. A set of four primers were designed based upon the conserved region of the 5.8S rRNA gene of members of the genus Alexandrium . Using this detection system, toxic Alexandrium genes were amplified and visualized as a ladder-like pattern of bands on agarose gels under isothermal condition within 60 min. The LAMP amplicons were also directly visualized by eye in the reaction tube by the addition of SYBR Green I. This LAMP assay was 10-fold more sensitive than a conventional PCR method with a detection limit of 5 cells per tube when targeting DNA from Alexandrium minutum . The LAMP assay reported here indicates the potential usefulness of the technique as a valuable simple, rapid alternative procedure for the detection of target toxic Alexandrium species during coastal water monitoring. 相似文献