全文获取类型
收费全文 | 6599篇 |
免费 | 443篇 |
国内免费 | 8篇 |
专业分类
7050篇 |
出版年
2023年 | 56篇 |
2022年 | 163篇 |
2021年 | 289篇 |
2020年 | 130篇 |
2019年 | 165篇 |
2018年 | 211篇 |
2017年 | 161篇 |
2016年 | 192篇 |
2015年 | 326篇 |
2014年 | 350篇 |
2013年 | 491篇 |
2012年 | 493篇 |
2011年 | 426篇 |
2010年 | 245篇 |
2009年 | 214篇 |
2008年 | 261篇 |
2007年 | 275篇 |
2006年 | 235篇 |
2005年 | 203篇 |
2004年 | 208篇 |
2003年 | 169篇 |
2002年 | 172篇 |
2001年 | 126篇 |
2000年 | 108篇 |
1999年 | 83篇 |
1998年 | 44篇 |
1997年 | 40篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1992年 | 63篇 |
1991年 | 74篇 |
1990年 | 74篇 |
1989年 | 62篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 56篇 |
1984年 | 49篇 |
1983年 | 43篇 |
1982年 | 27篇 |
1980年 | 33篇 |
1979年 | 39篇 |
1978年 | 43篇 |
1977年 | 33篇 |
1976年 | 34篇 |
1974年 | 40篇 |
1973年 | 27篇 |
1971年 | 25篇 |
1970年 | 27篇 |
排序方式: 共有7050条查询结果,搜索用时 15 毫秒
131.
V. Ramana Gopavajhula K. Viswanatha Chaitanya P. Akbar Ali Khan Jilani P. Shaik P. Narasimha Reddy Mohammad Alanazi 《Genetics and molecular biology》2013,36(2):225-236
Superoxide dismutase (SOD, EC 1.15.1.1) is an important metal-containing antioxidant enzyme that provides the first line of defense against toxic superoxide radicals by catalyzing their dismutation to oxygen and hydrogen peroxide. SOD is classified into four metalloprotein isoforms, namely, Cu/Zn SOD, Mn SOD, Ni SOD and Fe SOD. The structural models of soybean SOD isoforms have not yet been solved. In this study, we describe structural models for soybean Cu/Zn SOD, Mn SOD and Fe SOD and provide insights into the molecular function of this metal-binding enzyme in improving tolerance to oxidative stress in plants. 相似文献
132.
133.
Steven Rudeck Christelle Etard Muzamil M. Khan Wolfgang Rottbauer Rüdiger Rudolf Uwe Strhle Steffen Just 《Genesis (New York, N.Y. : 2000)》2016,54(8):431-438
Summary: Gene therapeutic approaches to cure genetic diseases require tools to express the rescuing gene exclusively within the affected tissues. Viruses are often chosen as gene transfer vehicles but they have limited capacity for genetic information to be carried and transduced. In addition, to avoid off‐target effects the therapeutic gene should be driven by a tissue‐specific promoter in order to ensure expression in the target organs, tissues, or cell populations. The larger the promoter, the less space will be left for the respective gene. Thus, there is a need for small but tissue‐specific promoters. Here, we describe a compact unc45b promoter fragment of 195 bp that retains the ability to drive gene expression exclusively in skeletal and cardiac muscle in zebrafish and mouse. Remarkably, the described unc45b promoter fragment not only drives muscle‐specific expression but presents heat‐shock inducibility, allowing a temporal and spatial quantity control of (trans)gene expression. Here, we demonstrate that the transgenic expression of the smyd1b gene driven by the unc45b promoter fragment is able to rescue the embryonically lethal heart and skeletal muscle defects in smyd1b‐deficient flatline mutant zebrafish. Our findings demonstrate that the described muscle‐specific unc45b promoter fragment might be a valuable tool for the development of genetic therapies in patients suffering from myopathies. genesis 54:431–438, 2016. © 2016 The Authors. Genesis Published by Wiley Periodicals, Inc. 相似文献
134.
Khan A Iqbal Z Watson DG Khan A Khan I Muhammad N Muhammad S Nasib HA Iqbal N Faiz-Ur-Rehman Kashif M 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2011,879(20):1725-1731
A fast, simple, and a reliable high-performance liquid chromatography linked with electrochemical detector (HPLC-ECD) method for the assessment of lipoic acid (LA) and dihydrolipoic acid (DHLA) in plasma was developed using naproxen sodium as an internal standard (IS) and validated according to standard guidelines. Extraction of both analytes and IS from plasma (250 μl) was carried out with a single step liquid-liquid extraction applying dichloromethane. The separated organic layer was dried under stream of nitrogen at 40°C and the residue was reconstituted with the mobile phase. Complete separation of both compounds and IS at 30°C on Discovery HS C18 RP column (250 mm × 4.6 mm, 5 μm) was achieved in 9 min using acetonitrile: 0.05 M phosphate buffer (pH 2.4 adjusted with phosphoric acid) (52:48, v/v) as a mobile phase pumped at flow rate of 1.5 ml min(-1) using electrochemical detector in DC mode at the detector potential of 1.0 V. The limit of detection and limit of quantification for lipoic acid were 500 pg/ml and 3 ng/ml, and for dihydrolipoic acid were 3 ng/ml and 10 ng/ml, respectively. The absolute recoveries of lipoic acid and dihydrolipoic acid determined on three nominal concentrations were in the range of 93.40-97.06, and 93.00-97.10, respectively. Similarly coefficient of variations (% CV) for both intra-day and inter-day were between 0.829 and 3.097% for lipoic acid and between 1.620 and 5.681% for dihydrolipoic acid, respectively. This validated method was applied for the analysis of lipoic acid/dihydrolipoic acid in the plasma of human volunteers and will be used for the quantification of these compounds in patients with oxidative stress induced pathologies. 相似文献
135.
Binyamin R Aslam Khan M Khan AI Azam Khan M Awan FS Khan NA 《Genetics and molecular research : GMR》2011,10(3):1681-1688
Urdbean (Vigna mungo) is an important pulse crop grown worldwide. Urdbean leaf crinkle virus (ULCV) is a pathogen of urdbean found in Pakistan that causes huge losses in yield. Forty urdbean varieties/lines were screened against the virus under field conditions during spring season 2009. None of the lines appeared to be highly resistant or resistant. On the basis of a 0-5 disease rating scale and disease severity index, genotypes varied significantly in their reaction to ULCV. Four lines (M-6206, IAM-382-15, IAM-133, and Mash-1) were moderately resistant, eight were rated as moderately susceptible, and 21 as susceptible; the remaining seven lines were highly susceptible. RAPD analyses revealed an extensive amount of variation, which could be used for cultivar identification. Genetic differentiation among urdbean genotypes was similar to the field screening data. The varieties 6065-3 and 6206 were highly susceptible and moderately resistant, respectively, to ULCV under field conditions, confirmed by the RAPD analysis. These varieties were the most diverse varieties in the similarity matrix (67.2%), while the varieties IAM-382-9 and 07M003 were the most similar (98.4%). This information will help in the recognition of available resistant germplasms that can resist this disease and will be utilized for urdbean improvement in Pakistan. 相似文献
136.
Solubilization and partial characterization of the sex hormone-binding globulin receptor from human prostate 总被引:1,自引:0,他引:1
The sex hormone-binding globulin (SHBG) receptor was solubilized from the membranes of human prostate glands with the zwitterionic detergent CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonic acid). The binding activity of the soluble receptor was measured by allowing it to bind to 125I-SHBG and precipitating the complex with polyethylene glycol-8000. The binding activity was stable for at least 4 months at -20 degrees C and had a half-life of 23 days at 4 degrees C. Like the membrane-bound receptor, Scatchard analysis revealed two sets of binding sites for the soluble one. At equilibrium (24 h), the high affinity site had an association constant (KA) of 6.8 x 10(8) M-1 and a binding capacity of 1.4 pmol/mg protein, whereas the low affinity site had a KA of 4.7 x 10(6) M-1 and a binding capacity of 43 pmol/mg protein. At 37 degrees C, the association rate constant (k1) was 8.37 x 10(5) M-1 min-1 and the dissociation rate constant (k2) was 3.43 x 10(-4) min-1. The soluble receptor was retarded on Sepharose CL-6B and had an apparent Mr = 167,000. 相似文献
137.
Boron is an essential plant micronutrient, but it is phytotoxic if present in excessive amounts in soil for certain plants
such as Artemisia annua L. that contains artemisinin (an important antimalarial drug) in its areal parts. Artemisinin is a sesquiterpene lactone
with an endoperoxide bridge. It is quite expensive compound because the only commercial source available is A. annua and the compound present in the plant is in very low concentration. Since A. annua is a major source of the antimalarial drug and B stress is a deadly threat to its cultivation, the present research was conducted
to determine whether the exogenous application of methyl jasmonate (MeJA) could combat the ill effects of excessive B present
in the soil. According to the results obtained, the B toxicity induced oxidative stress and reduced the stem height as well
as fresh and dry masses of the plant remarkably. The excessive amounts of soil B also lowered the net photosynthetic rate,
stomatal conductance, internal CO2 concentration and total chlorophyll content in the leaves. In contrast, the foliar application of MeJA enhanced the growth
and photosynthetic efficiency both in the stressed and non-stressed plants. The excessive B levels also increased the activities
of antioxidant enzymes, such as catalase, peroxidase and superoxide dismutase. Endogenous H2O2 and O2− levels were also high in the stressed plants. However, the MeJA application to the stressed plants reduced the amount of
lipid peroxidation and stimulated the synthesis of antioxidant enzymes, enhancing the content and yield of artemisinin as
well. Thus, it was concluded that MeJA might be utilized in mitigating the B toxicity and improving the content and yield
of artemisinin in A. annua plant. 相似文献
138.
Badshah A Subhan F Rauf K Bukhari NI Shah K Khan S Ahmed Z Khan I 《AAPS PharmSciTech》2011,12(2):525-533
Controlled-release (CR) matrix tablet of 4 mg risperidone was developed using flow bound dry granulation–slugging method to improve its safety profile and compliance. Model formulations F1, F2, and F3, consisting of distinct blends of Methocel® K100 LV-CR and Ethocel® standard 7FP premium, were slugged. Each batch of granules (250–1,000 μm), obtained by crushing the slugs, was divided into three portions after lubrication and then compressed to 9-, 12-, and 15-kg hard tablets. In vitro drug release studies were carried out in 0.1 N HCl (pH 1.2) and phosphate buffer (pH 6.8) using a paddle dissolution apparatus run at 50 rpm. The CR test tablet, containing 30% Methocel® and 60% Ethocel® (F3) with 12-kg hardness, exhibited pH-independent zero-order release kinetics for 24 h. The drug release rate was inversely proportional to the content of Ethocel®, while the gel layer formed of Methocel® helped in maintaining the integrity of the matrix. Changes in the hardness of tablet did not affect the release kinetics. The tablets were reproducible and stable for 6 months at 40 ± 2°C/75 ± 5% relative humidity. Risperidone and its active metabolite, 9-hydroxyrisperidone, present in the pooled rabbit’s serum, were analyzed with HPLC-UV at λmax 280 nm. The CR test tablet exhibited bioequivalence to reference conventional tablet in addition to the significantly (p < 0.05) optimized peak concentration, Cmax, and extended peak time, Tmax, of the active moiety. There was a good association between drug absorption in vivo and drug release in vitro (R2 = 0.7293). The successfully developed CR test tablet may be used for better therapeutic outcomes of risperidone.KEY WORDS: controlled release, dry granulation slugging method, risperidone 相似文献
139.
P. Sahab Khan K. P. Skandhan K. Ajesh M. V. P. Siraj 《Biological trace element research》2011,142(3):302-308
The study included evaluation of semen from normal, healthy adults and estimation of gold in seminal plasma from two regions
Nilambur valley (Malappuram District, Kerala Province, India; n = 11), where gold deposit is present and Kollam town (Kerala Province, India; n = 13) where gold is not present in soil. All samples showed normal spermiogram. Gold was estimated in seminal plasma by employing
inductively coupled plasma emission spectrophotometry. It varied from 0.23–1.15 ppm with mean 0.68 ppm in study area while
in control area it was 0.13–0.71 ppm with a mean of 0.41 ppm. Statistical studies (independent ‘t’ test) showed significantly high level (p < 0.05) of gold in seminal plasma from study area. ANOVA test proved that gold in seminal plasma is a significant (p < 0.05) factor for total spermatozoa count and its percentage of motility. 相似文献
140.
Huq A Sack RB Nizam A Longini IM Nair GB Ali A Morris JG Khan MN Siddique AK Yunus M Albert MJ Sack DA Colwell RR 《Applied and environmental microbiology》2005,71(8):4645-4654
The occurrence of outbreaks of cholera in Africa in 1970 and in Latin America in 1991, mainly in coastal communities, and the appearance of the new serotype Vibrio cholerae O139 in India and subsequently in Bangladesh have stimulated efforts to understand environmental factors influencing the growth and geographic distribution of epidemic Vibrio cholerae serotypes. Because of the severity of recent epidemics, cholera is now being considered by some infectious disease investigators as a "reemerging" disease, prompting new work on the ecology of vibrios. Epidemiological and ecological surveillance for cholera has been under way in four rural, geographically separated locations in Bangladesh for the past 4 years, during which both clinical and environmental samples were collected at biweekly intervals. The clinical epidemiology portion of the research has been published (Sack et al., J. Infect. Dis. 187:96-101, 2003). The results of environmental sampling and analysis of the environmental and clinical data have revealed significant correlations of water temperature, water depth, rainfall, conductivity, and copepod counts with the occurrence of cholera toxin-producing bacteria (presumably V. cholerae). The lag periods between increases or decreases in units of factors, such as temperature and salinity, and occurrence of cholera correlate with biological parameters, e.g., plankton population blooms. The new information on the ecology of V. cholerae is proving useful in developing environmental models for the prediction of cholera epidemics. 相似文献