全文获取类型
收费全文 | 5435篇 |
免费 | 424篇 |
国内免费 | 274篇 |
专业分类
6133篇 |
出版年
2024年 | 6篇 |
2023年 | 62篇 |
2022年 | 141篇 |
2021年 | 253篇 |
2020年 | 175篇 |
2019年 | 207篇 |
2018年 | 188篇 |
2017年 | 135篇 |
2016年 | 211篇 |
2015年 | 342篇 |
2014年 | 385篇 |
2013年 | 414篇 |
2012年 | 505篇 |
2011年 | 444篇 |
2010年 | 270篇 |
2009年 | 243篇 |
2008年 | 267篇 |
2007年 | 243篇 |
2006年 | 189篇 |
2005年 | 176篇 |
2004年 | 166篇 |
2003年 | 120篇 |
2002年 | 109篇 |
2001年 | 106篇 |
2000年 | 93篇 |
1999年 | 99篇 |
1998年 | 40篇 |
1997年 | 51篇 |
1996年 | 41篇 |
1995年 | 38篇 |
1994年 | 29篇 |
1993年 | 33篇 |
1992年 | 41篇 |
1991年 | 37篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1971年 | 9篇 |
1968年 | 5篇 |
排序方式: 共有6133条查询结果,搜索用时 15 毫秒
121.
2000a间,中国境内野生稻分布区域由2495575km2缩减至1371094km2,减少了45.06%;分布纬度北界由38°3′N南移至28°14′N,南移9°49′、1140km;中国境内栽培稻分布区域由4081860km2增加至9600000km2,增加了135.00%;分布北界由38°N北移至53°29′N,北移15°29′、1700km。人口分布重心主要在黄河流域和长江流域,对该区域野生稻的生存产生不利影响。而促进栽培稻的发展,必须建立野生稻自然保护区。 相似文献
122.
Bret Wankel Jiangyong Ouyang Xuemei Guo Krassimira Hadjiolova Jeremy Miller Yi Liao Daniel Kai Long Tham Rok Romih Leonardo R. Andrade Iwona Gumper Jean-Pierre Simon Rakhee Sachdeva Tanya Tolmachova Miguel C. Seabra Mitsunori Fukuda Nicole Schaeren-Wiemers Wan Jin Hong David D. Sabatini Xue-Ru Wu Xiangpeng Kong Gert Kreibich Michael J. Rindler Tung-Tien Sun 《Molecular biology of the cell》2016,27(10):1621-1634
Uroplakins (UPs) are major differentiation products of urothelial umbrella cells and play important roles in forming the permeability barrier and in the expansion/stabilization of the apical membrane. Further, UPIa serves as a uropathogenic Escherichia coli receptor. Although it is understood that UPs are delivered to the apical membrane via fusiform vesicles (FVs), the mechanisms that regulate this exocytic pathway remain poorly understood. Immunomicroscopy of normal and mutant mouse urothelia show that the UP-delivering FVs contained Rab8/11 and Rab27b/Slac2-a, which mediate apical transport along actin filaments. Subsequently a Rab27b/Slp2-a complex mediated FV–membrane anchorage before SNARE-mediated and MAL-facilitated apical fusion. We also show that keratin 20 (K20), which forms a chicken-wire network ∼200 nm below the apical membrane and has hole sizes allowing FV passage, defines a subapical compartment containing FVs primed and strategically located for fusion. Finally, we show that Rab8/11 and Rab27b function in the same pathway, Rab27b knockout leads to uroplakin and Slp2-a destabilization, and Rab27b works upstream from MAL. These data support a unifying model in which UP cargoes are targeted for apical insertion via sequential interactions with Rabs and their effectors, SNAREs and MAL, and in which K20 plays a key role in regulating vesicular trafficking. 相似文献
123.
Synergistic effect of cadmium chloride and acetaldehyde on cytotoxicity and its prevention by quercetin and glycyrrhizin 总被引:3,自引:0,他引:3
Cadmium chloride at concentrations of 10-50mM and acetaldehyde (AA) at 1-5mM showed synergistic toxic effects on V79 cells in vitro. Furthermore, synergistic effects of these chemicals were also observed in mutagenicities of the Hprt gene within certain dose ranges (cadmium chloride 5-10mM, and AA 1-2.5mM). Moreover, lipid peroxide formation, malondialdehyde (MDA) formation, detected by 2-thiobarbituric acid (TBA) reaction and the mitochondrial membrane potentials detected by rhodamine 123 uptake were significantly increased with the combined effect of cadmium and AA in V79. Thus, the cytotoxicity and genotoxicity displayed by combination of these chemicals can be considered to be associated with oxidative stress. Further, these effects were efficiently reduced by quercetin and less efficiently with glycyrrhizin. 相似文献
124.
Chun Fu Lin Sanford P. C. Hsu Chung Jung Lin Wan Yuo Guo Chih Hsiang Liao Wei Fa Chu Sheng Che Hung Yang Shin Shih Yen Tzu Lin 《PloS one》2016,11(3)
Purpose
We sought to imitate angiographic cerebral circulation time (CCT) and create a similar index from baseline CT perfusion (CTP) to better predict vasospasm in patients with subarachnoid hemorrhage (SAH).Methods
Forty-one SAH patients with available DSA and CTP were retrospectively included. The vasospasm group was comprised of patients with deterioration in conscious functioning and newly developed luminal narrowing; remaining cases were classified as the control group. The angiography CCT (XA-CCT) was defined as the difference in TTP (time to peak) between the selected arterial ROIs and the superior sagittal sinus (SSS). Four arterial ROIs were selected to generate four corresponding XA-CCTs: the right and left anterior cerebral arteries (XA-CCTRA2 and XA-CCTLA2) and right- and left-middle cerebral arteries (XA-CCTRM2 and XA-CCTLM2). The CCTs from CTP (CT-CCT) were defined as the differences in TTP from the corresponding arterial ROIs and the SSS. Correlations of the different CCTs were calculated and diagnostic accuracy in predicting vasospasm was evaluated.Results
Intra-class correlations ranged from 0.96 to 0.98. The correlations of XA-CCTRA2, XA-CCTRM2, XA-CCTLA2, and XA-CCTLM2 with the corresponding CT-CCTs were 0.64, 0.65, 0.53, and 0.68, respectively. All CCTs were significantly prolonged in the vasospasm group (5.8–6.4 s) except for XA-CCTLA2. CT-CCTA2 of 5.62 was the optimal cut-off value for detecting vasospasm with a sensitivity of 84.2% and specificity 82.4%Conclusion
CT-CCTs can be used to interpret cerebral flow without deconvolution algorithms, and outperform both MTT and TTP in predicting vasospasm risk. This finding may help facilitate management of patients with SAH. 相似文献125.
Hu Su Chao Yu Junjun Shang Xin Yan Pengfei Liao Youlin Zhu Yanchun Gong Bin Zeng 《Acta Physiologiae Plantarum》2016,38(7):178
The aim of this study was to investigate the effect of phenylalanine ammonia lyase (PAL) and isochorismate synthase (ICS) on free salicylic acid (FSA) or total salicylic acid (TSA) content, and the effect of endogenous SA on baicalin and baicalein accumulation in Scutellaria baicalensis Georgi, respectively. We amplified partial sequences of PAL and ICS genes in Scutellaria baicalensis Georgi and silenced the two genes with virus-induced gene silence (VIGS) technique, respectively. The influence of gene silence on FSA, TSA, baicalin, and baicalein accumulation in Scutellaria baicalensis Georgi were analyzed, and these parameters were also investigated under high temperature. Results indicated that PAL silence significantly affected the FSA, ICS affected TSA content. FSA significantly affected the baicalin, rather than baicalein content. Our results along with previous studies indicated PAL and ICS were different in the regulation of FSA or TSA synthesis, and FSA and TSA were different in the regulation of baicalin and baicalein synthesis in Scutellaria baicalensis Georgi. 相似文献
126.
缺血预处理对缺血再灌注后兔脊髓磷酸腺苷代谢的影响 总被引:5,自引:0,他引:5
目的:研究缺血参处理对缺血再灌注后兔脊髓磷酸腺苷代谢的影响。方法:往置入腹主动脉的Swan-Ganz导管气囊内注气造成兔腰髓缺血模型。将实验兔分为假手术组、缺血组和预处理组。应用反相高效液相色谱方法(reverse phase HPLC),对缺血再灌注后不同时间点腰髓组织中磷酸腺苷(ATP、ADP、AMP)的含量进行检测。结果:和假手术组相比,缺血组兔再灌后各时间点腰髓组织ATP含量有明显下降(P<0.01)。与缺血组相应时间点相比,预处理组兔再灌注后腰髓组织ATP含量明显提高(P<0.01)。结论:缺血预处理显著提高缺血再灌注后兔脊髓组织ATP含量,这可能是缺血预处理对脊髓缺血再灌注损伤产生保护作用的机制之一。 相似文献
127.
Bonsignori M Hwang KK Chen X Tsao CY Morris L Gray E Marshall DJ Crump JA Kapiga SH Sam NE Sinangil F Pancera M Yongping Y Zhang B Zhu J Kwong PD O'Dell S Mascola JR Wu L Nabel GJ Phogat S Seaman MS Whitesides JF Moody MA Kelsoe G Yang X Sodroski J Shaw GM Montefiori DC Kepler TB Tomaras GD Alam SM Liao HX Haynes BF 《Journal of virology》2011,85(19):9998-10009
V2/V3 conformational epitope antibodies that broadly neutralize HIV-1 (PG9 and PG16) have been recently described. Since an elicitation of previously known broadly neutralizing antibodies has proven elusive, the induction of antibodies with such specificity is an important goal for HIV-1 vaccine development. A critical question is which immunogens and vaccine formulations might be used to trigger and drive the development of memory B cell precursors with V2/V3 conformational epitope specificity. In this paper we identified a clonal lineage of four V2/V3 conformational epitope broadly neutralizing antibodies (CH01 to CH04) from an African HIV-1-infected broad neutralizer and inferred their common reverted unmutated ancestor (RUA) antibodies. While conformational epitope antibodies rarely bind recombinant Env monomers, a screen of 32 recombinant envelopes for binding to the CH01 to CH04 antibodies showed monoclonal antibody (MAb) binding to the E.A244 gp120 Env and to chronic Env AE.CM243; MAbs CH01 and CH02 also bound to transmitted/founder Env B.9021. CH01 to CH04 neutralized 38% to 49% of a panel of 91 HIV-1 tier 2 pseudoviruses, while the RUAs neutralized only 16% of HIV-1 isolates. Although the reverted unmutated ancestors showed restricted neutralizing activity, they retained the ability to bind to the E.A244 gp120 HIV-1 envelope with an affinity predicted to trigger B cell development. Thus, E.A244, B.9021, and AE.CM243 Envs are three potential immunogen candidates for studies aimed at defining strategies to induce V2/V3 conformational epitope-specific antibodies. 相似文献
128.
Zhang Q Chen D Lin J Liao R Tong W Xu Z Liu W 《The Journal of biological chemistry》2011,286(24):21287-21294
The radical S-adenosylmethionine (AdoMet) enzyme superfamily is remarkable at catalyzing chemically diverse and complex reactions. We have previously shown that NosL, which is involved in forming the indole side ring of the thiopeptide nosiheptide, is a radical AdoMet enzyme that processes L-Trp to afford 3-methyl-2-indolic acid (MIA) via an unusual fragmentation-recombination mechanism. We now report the expansion of the MIA synthase family by characterization of NocL, which is involved in nocathiacin I biosynthesis. EPR and UV-visible absorbance spectroscopic analyses demonstrated the interaction between L-Trp and the [4Fe-4S] cluster of NocL, leading to the assumption of nonspecific interaction of [4Fe-4S] cluster with other nucleophiles via the unique Fe site. This notion is supported by the finding of the heterogeneity in the [4Fe-4S] cluster of NocL in the absence of AdoMet, which was revealed by the EPR study at very low temperature. Furthermore, a free radical was observed by EPR during the catalysis, which is in good agreement with the hypothesis of a glycyl radical intermediate. Combined with the mutational analysis, these studies provide new insights into the function of the [4Fe-4S] cluster of radical AdoMet enzymes as well as the mechanism of the radical-mediated complex carbon chain rearrangement catalyzed by MIA synthase. 相似文献
129.
Sarcocystis cymruensis was initially identified in skeletal muscles of 22 (11.6%) of 189 wild rats (Rattus spp.) captured in 2008 in Anning and Kunming, Peoples Republic of China. Sarcocyst walls were thin (<1 μm) and smooth. Ultrastructurally, the parasitophorous vacuolar membrane had small, osmiophilic knob-like invaginations covered with numerous vesicle-like invaginations toward the interior of the cyst. Domestic cats (Felis catus) fed sarcocysts shed sporocysts measuring 10.3 (9.8-11.0) × 7.6 (7.2-9.5) μm with a prepatent period of 6 to 8 days. Sarcocysts were infective orally to Norway rats, and oocysts and sporocysts developed in the lamina propria of the small intestine of rats fed sarcocysts. Thus, rats were both intermediate and definitive hosts for S. cymruensis. 相似文献
130.
Liao YC Huang TW Chen FC Charusanti P Hong JS Chang HY Tsai SF Palsson BO Hsiung CA 《Journal of bacteriology》2011,193(7):1710-1717
Klebsiella pneumoniae is a Gram-negative bacterium of the family Enterobacteriaceae that possesses diverse metabolic capabilities: many strains are leading causes of hospital-acquired infections that are often refractory to multiple antibiotics, yet other strains are metabolically engineered and used for production of commercially valuable chemicals. To study its metabolism, we constructed a genome-scale metabolic model (iYL1228) for strain MGH 78578, experimentally determined its biomass composition, experimentally determined its ability to grow on a broad range of carbon, nitrogen, phosphorus and sulfur sources, and assessed the ability of the model to accurately simulate growth versus no growth on these substrates. The model contains 1,228 genes encoding 1,188 enzymes that catalyze 1,970 reactions and accurately simulates growth on 84% of the substrates tested. Furthermore, quantitative comparison of growth rates between the model and experimental data for nine of the substrates also showed good agreement. The genome-scale metabolic reconstruction for K. pneumoniae presented here thus provides an experimentally validated in silico platform for further studies of this important industrial and biomedical organism. 相似文献