全文获取类型
收费全文 | 35927篇 |
免费 | 2929篇 |
国内免费 | 3019篇 |
出版年
2024年 | 63篇 |
2023年 | 390篇 |
2022年 | 1069篇 |
2021年 | 1934篇 |
2020年 | 1363篇 |
2019年 | 1608篇 |
2018年 | 1541篇 |
2017年 | 1149篇 |
2016年 | 1574篇 |
2015年 | 2214篇 |
2014年 | 2639篇 |
2013年 | 2901篇 |
2012年 | 3308篇 |
2011年 | 2962篇 |
2010年 | 1825篇 |
2009年 | 1704篇 |
2008年 | 1894篇 |
2007年 | 1664篇 |
2006年 | 1441篇 |
2005年 | 1265篇 |
2004年 | 946篇 |
2003年 | 918篇 |
2002年 | 784篇 |
2001年 | 563篇 |
2000年 | 531篇 |
1999年 | 555篇 |
1998年 | 317篇 |
1997年 | 310篇 |
1996年 | 317篇 |
1995年 | 287篇 |
1994年 | 270篇 |
1993年 | 197篇 |
1992年 | 250篇 |
1991年 | 185篇 |
1990年 | 189篇 |
1989年 | 132篇 |
1988年 | 112篇 |
1987年 | 88篇 |
1986年 | 85篇 |
1985年 | 83篇 |
1984年 | 50篇 |
1983年 | 36篇 |
1982年 | 37篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
11.
Qibo Jiang Shuguang Li 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,727(1-2)
Gabapentin (GBP) is a new antiepileptic drug approved for clinical treatment of partial seizures in the USA. Serum GBP concentrations in 283 patients were studied using high-performance liquid chromatography with fluorescence detection. The standard curves were linear over a range of 60 ng to 15 μg/ml. The coefficient of variations were 3.4 to 8.8% and 1.4 to 9.8% for intra- and inter-assay studies, respectively. The lower limit of quantitation was 10 ng/ml. Of the 283 patients studied, 72.5% had GBP levels between 2 and 10 μg/ml, 14.8% were below 2 μg/ml and 12.7% above 10 μg/ml. The mean±S.E. of GBP in 283 patients was 5.38±0.23 μg/ml. Peak concentrations of more than 15 μg/ml and trough levels as low as 0.1 μg/ml were not uncommon. The method described was rapid, simple, highly sensitive and reproducible. Other antiepileptic drugs and endogenous compounds did not interfere with the assay. 相似文献
12.
13.
14.
15.
16.
Y. Jiang 《Biochimica et Biophysica Acta (BBA)/General Subjects》1994,1201(1):76-84
Proteolysis of the hydroxylase component of soluble methane monooxygenase (MMO) with trypsin yielded a protein which retained 50% activity in a standard MMO assay. In an H2O2-driven assay, in which H2O2 replaced two of the protein components, NADH and O2 used in the standard assay, the proteolysed hydroxylase retained full activity for ethane, propane and propene, but had a 2–3 fold increase with methane as substrate. Several crosslinking reagents have been tested for their ability to stabilise the proteolysed form of the hydroxylase. Using polyoxyethylene bis(imidazolyl carbonyl) (Mr 3350) as the crosslinking agent, increased thermostability of the hydroxylase was observed. Activated methoxypolyethylene glycol (Mr 5000) was used to modify the hydroxylase which was now soluble in organic solvents as well as water and could be activated by H2O2. The glycol-modified hydroxylase functioned well in organic solvents in the catalysis of propene oxidation. 相似文献
17.
18.
19.
Karen Castillioni Kevin Wilcox Lifen Jiang Yiqi Luo Chang Gyo Jung Lara Souza 《Ecology and evolution》2020,10(13):6702-6713
- Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
- We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
- We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
- Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
- Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.
20.
Background: Little is known about geographic variations in liver cancer at high incident regions. We aimed to identify spatial variation of hepatocellular carcinoma (HCC) at a high-risk area in China and determine its association with socioeconomic status (SES). Methods: Based on 2299 liver cancer cases diagnosed in Haimen from 2003 to 2006, we calculated age–sex standardized incidence ratios (SIRs) and used two spatial scan statistics to determine the geographic variations in HCC. Bayesian hierarchical model was used to explore the association between HCC incidence and SES. Results: Age and sex SIRs for HCC varied from 0.54 to 1.97 for 24 townships. The eastern region of Haimen was identified to have a significantly increased risk of HCC. Fitting of a Bayesian hierarchical model linking per-capita fiscal revenue with SIRs of HCC indicated that the area with a lower revenue had a significantly higher incidence of HCC [βlog(revenue) = ?0.179, posterior 95% Bayesian credible interval (CI) = (?0.326, ?0.04)]. Conclusions: This study demonstrated substantial geographic variation in the incidence of HCC within a high-risk region, which was associated with SES. HCC control and intervention should focus on disadvantaged areas to reduce the HCC disparities. 相似文献