全文获取类型
收费全文 | 21528篇 |
免费 | 2041篇 |
国内免费 | 3609篇 |
专业分类
27178篇 |
出版年
2024年 | 77篇 |
2023年 | 295篇 |
2022年 | 654篇 |
2021年 | 987篇 |
2020年 | 775篇 |
2019年 | 977篇 |
2018年 | 930篇 |
2017年 | 721篇 |
2016年 | 935篇 |
2015年 | 1373篇 |
2014年 | 1705篇 |
2013年 | 1686篇 |
2012年 | 2136篇 |
2011年 | 1923篇 |
2010年 | 1250篇 |
2009年 | 1151篇 |
2008年 | 1383篇 |
2007年 | 1221篇 |
2006年 | 1183篇 |
2005年 | 947篇 |
2004年 | 812篇 |
2003年 | 789篇 |
2002年 | 599篇 |
2001年 | 321篇 |
2000年 | 305篇 |
1999年 | 288篇 |
1998年 | 212篇 |
1997年 | 170篇 |
1996年 | 150篇 |
1995年 | 116篇 |
1994年 | 118篇 |
1993年 | 76篇 |
1992年 | 98篇 |
1991年 | 78篇 |
1990年 | 74篇 |
1989年 | 66篇 |
1988年 | 45篇 |
1987年 | 38篇 |
1986年 | 37篇 |
1985年 | 48篇 |
1984年 | 53篇 |
1983年 | 37篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1975年 | 23篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
A novel nanocomposite synthesis method of amino-modified NaYF(4):Yb,Er upconversion luminescent nanoparticles and single-walled carbon nanohorns was developed via covalent linkage for the first time. The nanocomposite was covalently coupled with rabbit anti-CEA8 antibody and then used successfully as a cell labeling agent for the immunolabeling and imaging of HeLa cells. 相似文献
882.
Kiryluk K Li Y Sanna-Cherchi S Rohanizadegan M Suzuki H Eitner F Snyder HJ Choi M Hou P Scolari F Izzi C Gigante M Gesualdo L Savoldi S Amoroso A Cusi D Zamboli P Julian BA Novak J Wyatt RJ Mucha K Perola M Kristiansson K Viktorin A Magnusson PK Thorleifsson G Thorsteinsdottir U Stefansson K Boland A Metzger M Thibaudin L Wanner C Jager KJ Goto S Maixnerova D Karnib HH Nagy J Panzer U Xie J Chen N Tesar V Narita I Berthoux F Floege J Stengel B Zhang H Lifton RP Gharavi AG 《PLoS genetics》2012,8(6):e1002765
IgA nephropathy (IgAN), major cause of kidney failure worldwide, is common in Asians, moderately prevalent in Europeans, and rare in Africans. It is not known if these differences represent variation in genes, environment, or ascertainment. In a recent GWAS, we localized five IgAN susceptibility loci on Chr.6p21 (HLA-DQB1/DRB1, PSMB9/TAP1, and DPA1/DPB2 loci), Chr.1q32 (CFHR3/R1 locus), and Chr.22q12 (HORMAD2 locus). These IgAN loci are associated with risk of other immune-mediated disorders such as type I diabetes, multiple sclerosis, or inflammatory bowel disease. We tested association of these loci in eight new independent cohorts of Asian, European, and African-American ancestry (N = 4,789), followed by meta-analysis with risk-score modeling in 12 cohorts (N = 10,755) and geospatial analysis in 85 world populations. Four susceptibility loci robustly replicated and all five loci were genome-wide significant in the combined cohort (P = 5×10−32–3×10−10), with heterogeneity detected only at the PSMB9/TAP1 locus (I2 = 0.60). Conditional analyses identified two new independent risk alleles within the HLA-DQB1/DRB1 locus, defining multiple risk and protective haplotypes within this interval. We also detected a significant genetic interaction, whereby the odds ratio for the HORMAD2 protective allele was reversed in homozygotes for a CFHR3/R1 deletion (P = 2.5×10−4). A seven–SNP genetic risk score, which explained 4.7% of overall IgAN risk, increased sharply with Eastward and Northward distance from Africa (r = 0.30, P = 3×10−128). This model paralleled the known East–West gradient in disease risk. Moreover, the prediction of a South–North axis was confirmed by registry data showing that the prevalence of IgAN–attributable kidney failure is increased in Northern Europe, similar to multiple sclerosis and type I diabetes. Variation at IgAN susceptibility loci correlates with differences in disease prevalence among world populations. These findings inform genetic, biological, and epidemiological investigations of IgAN and permit cross-comparison with other complex traits that share genetic risk loci and geographic patterns with IgAN. 相似文献
883.
固定化微生物处理模拟污染地表水 总被引:1,自引:0,他引:1
以聚乙烯醇和海藻酸钠为包埋剂、驯化后的活性污泥为包埋菌剂,制备固定化微生物颗粒,其中包埋剂与包埋菌剂的比例为2:1。将该固定化微生物颗粒按20%的填充率装填到自制反应器中,用于处理模拟污染地表水,研究该固定化微生物的性能特点及其对模拟污染地表水的净化效果。结果表明:固定化微生物反应器的最佳水力停留时间为10h,最佳进水COD负荷为1.15~1.85g·L-1·d-1。在水温为20~29℃、溶解氧为3~4mg·L-1、水力停留时间为10h的条件下,当进水COD浓度为70.58~91.76mg·L-1、铵氮浓度为13.68~17.82mg·L-1时,COD去除率>62.3%,铵氮去除率>90.6%,表明固定化微生物能够有效地去除污染地表水中的COD和铵氮。 相似文献
884.
885.
利用ISSR标记对新疆梭梭遗传多样性的研究 总被引:5,自引:0,他引:5
利用ISSR分子标记对新疆梭梭8个居群、218个个体进行了遗传多样性的比较分析,在供试材料中,11个引物共扩增出222个多态位点,多态位点百分率为89.23%,8个居群的多态位点百分率差异在23.42%~45.05%之间,多态位点百分率最高的是乌苏居群,最低的为托克逊居群.遗传变异分析表明,物种水平的基因分化系数Gst为63.78.居群间的基因流Nm为0.284 0,Shannon多样性指数(I)为0.506 0,物种水平的Nei s基因多样度(H)为0.336 2.遗传分析表明乌苏居群和莫索湾居群有较近的遗传距离. 相似文献
886.
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, 1) is a yellow ingredient isolated from turmeric (Curcumin longa). It has been shown to exhibit a variety of biological activities including antioxidative activity. In order to find more active antioxidants with 1 as the lead compound we synthesized curcumin analogues, i.e., 1,7-bis(3,4-dihydroxyphenyl)-1,6-heptadiene-3,5-dione (2), 1-(3,4-dihydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (3), 1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (4), 1,7-bis (4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (5), 1-(3,4-dimethoxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (6), 1,7-bis(3,4-dimethoxyphenyl)-1,6- heptadiene-3,5-dione (7), 1,7-bis(4-methoxyphenyl)-1,6-heptadiene-3,5-dione (8), and 1,7-diphenyl-1,6-heptadiene-3,5-dione (9). Antioxidative effects of curcumin and its analogues against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or by cupric ion (Cu2+). The reaction kinetics were monitored either by the uptake of oxygen and the depletion of alpha-tocopherol present in the native LDL, or by the formation of thiobarbituric acid reactive substances. Kinetic analysis of the antioxidation process demonstrates that these compounds, except 7, 8, and 9, are effective antioxidants against AAPH- and Cu2+ -initiated LDL peroxidation by H-atom abstraction from the phenolic groups. Compounds 2 and 3 which bear ortho-diphenoxyl functionality possess significantly higher antioxidant activity than curcumin and other analogues, and the 4-hydroxy-3-methoxyphenyl group also play an important role in the antioxidative activity. 相似文献
887.
In contrast to the epidermal growth factor (EGF) receptor, ErbB2 is known to remain at the plasma membrane after ligand binding and dimerization. However, why ErbB2 is not efficiently down-regulated has remained elusive. Basically, two possibilities exist: ErbB2 is internalization resistant or it is efficiently recycled after internalization. By a combination of confocal microscopy, immunogold labeling electron microscopy, and biochemical techniques we show that ErbB2 is preferentially associated with membrane protrusions. Moreover, it is efficiently excluded from clathrin-coated pits and is not seen in transferrin receptor-containing endosomes. This pattern is not changed after binding of EGF, heregulin, or herceptin. The exclusion from coated pits is so pronounced that it cannot just be explained by lack of an internalization signal. Although ErbB2 is a raft-associated protein, the localization of ErbB2 to protrusions is not a result of raft binding. Also, an intact actin cytoskeleton is not required for keeping ErbB2 away from coated pits. However, after efficient cross-linking, ErbB2 is removed from protrusions to occur on the bulk membrane, in coated pits, and in endosomes. These data show that ErbB2 is a remarkably internalization-resistant receptor and suggest that the mechanism underlying the firm association of ErbB2 with protrusions also is the reason for this resistance. 相似文献
888.
889.
膀胱ICC样细胞研究进展 总被引:1,自引:1,他引:1
Cajal间质细胞(ICC)是分布在消化道自主神经末梢和平滑肌之间的一类特殊细胞,是胃肠道慢波的起搏细胞,是胃肠运动的pacemaker,它推进电活动的传播以及介导神经信号传递,控制胃肠道自主神经运动功能.近年来在人和动物膀耽中已证实存在ICC样细胞,其功能研究是最近研究的热点.ICC样细胞证实具有和胃肠ICC一样的藕联及神经调节功能的结构基础和功能特点,其是否具有起搏特性值得期待. 相似文献
890.
对武汉东湖大型围隔和围栏中的水生植被和不同形态的磷近2年的调查分析结果表明:在围隔中的水生维管束植物得到恢复、生物量明显大于对照区的情况下,水中的总磷(TP)、溶解活性磷(DRP)、颗粒性磷(PP)浓度明显低于对照区,水生维管束植物的良好生长是导致磷浓度降低的主要因素,总溶解磷(TDP)、溶解非活性磷(DNP)浓度则与对照区无显著差异;围隔(栏)及对照区中TP、PP的浓度秋高冬低,TDP浓度秋、冬季较高,春、夏季较低,DNP浓度春季较高,冬季较低;TP中PP含量约为TDP的4-6倍,DRP与DNP的含量相近或稍有差别。 相似文献