全文获取类型
收费全文 | 31254篇 |
免费 | 2989篇 |
国内免费 | 2746篇 |
专业分类
36989篇 |
出版年
2024年 | 269篇 |
2023年 | 455篇 |
2022年 | 938篇 |
2021年 | 1511篇 |
2020年 | 1063篇 |
2019年 | 1308篇 |
2018年 | 1322篇 |
2017年 | 1031篇 |
2016年 | 1343篇 |
2015年 | 1945篇 |
2014年 | 2324篇 |
2013年 | 2447篇 |
2012年 | 2961篇 |
2011年 | 2717篇 |
2010年 | 1685篇 |
2009年 | 1487篇 |
2008年 | 1779篇 |
2007年 | 1555篇 |
2006年 | 1366篇 |
2005年 | 1161篇 |
2004年 | 1018篇 |
2003年 | 868篇 |
2002年 | 862篇 |
2001年 | 582篇 |
2000年 | 471篇 |
1999年 | 451篇 |
1998年 | 313篇 |
1997年 | 234篇 |
1996年 | 213篇 |
1995年 | 187篇 |
1994年 | 201篇 |
1993年 | 134篇 |
1992年 | 151篇 |
1991年 | 107篇 |
1990年 | 108篇 |
1989年 | 85篇 |
1988年 | 75篇 |
1987年 | 47篇 |
1986年 | 51篇 |
1985年 | 35篇 |
1984年 | 36篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1965年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Ryan A. Flynn Julia A. Belk Yanyan Qi Yuki Yasumoto Jin Wei Mia Madel Alfajaro Quanming Shi Maxwell R. Mumbach Aditi Limaye Peter C. DeWeirdt Cameron O. Schmitz Kevin R. Parker Elizabeth Woo Howard Y. Chang Tamas L. Horvath Jan E. Carette Carolyn R. Bertozzi Craig B. Wilen Ansuman T. Satpathy 《Cell》2021,184(9):2394-2411.e16
2.
正Dear Editor,The fall armyworm, Spodoptera frugiperda(Lepidoptera:Noctuidae), a highly agricultural destructive pest of cereals, is originally rampant in tropical and subtropical America(Kenis et al. 2019). The caterpillars of this moth feed on more than 350 plant species(Harrison et al. 2019), 相似文献
3.
T B Ng W Gao L Li S M Niu L Zhao J Liu L S Shi M Fu F Liu 《Biochimie et biologie cellulaire》2005,83(1):78-85
The effects of rose-flower extract on antioxidant enzymes were studied. The activities of catalase (CAT) and glutathione peroxidase (GPx) in 9-month-old senescence-accelerated mice (SAM mice) were lower than those in 6-month-old SAM mice. Therefore, 9-month-old SAM mice were the most appropriate targets for treatment with the rose-flower extract. The activities of CAT and GPx in SAM mice treated with rose-flower extract showed a marked increase in whole blood and liver. At the same time, the gene-expression level of CAT and GPx was upregulated in the liver, while malondialdehyde content in liver and brain decreased. Male SAM mice were more sensitive than female SAM mice. The mean and the longest lifespan of SAM mice were longer after treatment with rose-flower extract. 相似文献
4.
Eric J. Reardon 《中国科学:生命科学英文版》2005,48(Z1)
Hydrocalumite, a calcium aluminate hydrate phase, consists of positively-charged structure units, and is therefore an ideal candidate for accommodating anionic contaminants. In this study, a series of batch experiments was carried out to examine the uptake of chromate and selenate by hydrocalumite. To determine the uptake capacity and long-term stability, hydro-calumite solid solutions between chromate/selenate and hydroxyl were synthesized over a reaction time of more than one year. At a ratio of water to initial solids added (CaAl2O4+CaO) of 75 : 1, the maximum uptake capacities were over 77 and 114 g/kg for Cr and Se, respectively. These values are very close to the theoretical uptake capacities of chromate and selenate hydrocalumite end-members (81 and 118 g/kg, respectively). The oxyanion removal efficiency from solution was above 95%. Due to the high uptake capacity and anion removal efficiency of hy-drocalumites, their application in wastewater treatment is promising. Hydrocalumites are also impor 相似文献
5.
Colin J. Saunders Min Gao Jason A. Lynch Rudolf Jaffé Daniel L. Childers 《Hydrobiologia》2006,569(1):475-492
We measured the abundance of Cladium jamaicense (Crantz) seeds and three biomarkers in freshwater marsh soils in Shark River Slough (SRS), Everglades National Park (ENP)
to determine the degree to which these paleoecological proxies reflect spatial and temporal variation in vegetation. We found
that C. jamaicense seeds and the biomarkers Paq, total lignin phenols (TLP) and kaurenes analyzed from surface soils were all significantly correlated with extant aboveground
C. jamaicense biomass quantified along a vegetation gradient from a C. jamaicense to a wet prairie/slough (WPS) community. Our results also suggest that these individual proxies may reflect vegetation over
different spatial scales: Paq and kaurenes correlated most strongly (R
2 = 0.88 and 0.99, respectively) with vegetation within 1 m of a soil sample, while seeds and TLP reflected vegetation 0–20 m
upstream of soil samples. These differences in the spatial scale depicted by the different proxies may be complementary in
understanding aspects of historic landscape patterning. Soil profiles of short (25 cm) cores showed that downcore variation
in C. jamaicense seeds was highly correlated with two of the three biomarkers (Paq, R
2 = 0.84, p<0.005; TLP, R
2 = 0.97, p<0.0001), and all four of the proxies indicated a recent increase in C. jamaicense biomass at the site. Using a preliminary depth-to-age relationship based on matching charcoal peaks with available ENP fire
records (1980-present) specific to our coring site, we found that peak-depths in C. jamaicense seed concentration appeared to correspond to recent minimum water levels (e.g., 1989 and 2001), and low seed abundance corresponded
to high water levels (e.g., 1995), consistent with the known autecology of C. jamaicense. In summary, the combination of C. jamaicense seeds and biomarkers may be useful for paleoecological reconstruction of vegetation change and ultimately in guaging the
success of ongoing efforts to restore historic hydrologic conditions in the South Florida Everglades. 相似文献
6.
7.
8.
Many studies investigated the relationship between matrix metalloproteinase 2 (MMP-2) overexpression and survival in patients with colorectal cancer (CRC), but yielded inconsistent results. To derive a more precise estimate of the prognostic significance of MMP-2 overexpression, we reviewed published studies and carried out a meta-analysis. Eligible articles were identified for the period up to March 2012 in electronic databases. To evaluate the correlation between MMP-2 overexpression and the prognosis in CRC, pooled hazard ratio (HR) and its 95?% confidence interval (95?% CI) for poorer overall and progression-free survival were appropriately derived from fixed-effects or random-effects models using standard meta-analysis techniques. Thirteen studies with a total of 1,919 CRC patients stratifying overall survival (OS) and/or progression-free survival in CRC patients by MMP-2 expression status were eligible for analysis. Ten studies investigated the OS in a total of 1,612 cases with CRC, and five studies investigated the progression-free survival in a total of 508 patients CRC. The combined HR estimate for OS and progression-free survival was 1.74 (95?% CI, 1.34?C2.26) and 1.35 (95?% CI, 1.07?C1.80), respectively. Both subgroup analyses and sensitivity analysis further identified the prognostic role of MMP-2 overexpression in patients with CRC. There was no evidence for publication bias. In conclusion, MMP-2 overexpression is associated with poorer overall and progression-free survival in patients with CRC. 相似文献
9.
Yu-Cai He Cui-Luan Ma Zhen-Xing Yang Min Zhou Zhen Xing Jiang-Tao Ma Hui-Lei Yu 《Applied microbiology and biotechnology》2013,97(24):10329-10337
Enantiopure sulfoxides can be prepared via the asymmetric oxidation of sulfides using sulfide monooxygenases. The n-octane–water biphasic system was chosen for the bio-oxidation of a water-insoluble phenyl methyl sulfide (PMS) by Rhodococcus sp. CCZU10-1. In this n-octane–water system, the optimum reaction conditions were obtained. (S)-phenyl methyl sulfoxide ((S)-PMSO) with >99.9 % enantiomeric excess formed at 55.3 mM in the n-octane–water biphasic system. Using fed-batch method, a total of 118 mM (S)-PMSO accumulated in 1-L reaction mixture after the 7th feed, and no (R)-PMSO and sulfone were detected. Moreover, Rhodococcus sp. CCZU10-1 displayed fairly good activity and enantioselectivity toward other sulfides. In conclusion, Rhodococcus sp. CCZU10-1 is a promising biocatalyst for synthesizing highly optically active sulfoxides. 相似文献
10.