全文获取类型
收费全文 | 75726篇 |
免费 | 18939篇 |
国内免费 | 3783篇 |
专业分类
98448篇 |
出版年
2024年 | 128篇 |
2023年 | 696篇 |
2022年 | 1654篇 |
2021年 | 3014篇 |
2020年 | 3755篇 |
2019年 | 5595篇 |
2018年 | 5556篇 |
2017年 | 5321篇 |
2016年 | 6017篇 |
2015年 | 6938篇 |
2014年 | 7226篇 |
2013年 | 7863篇 |
2012年 | 6443篇 |
2011年 | 5588篇 |
2010年 | 5393篇 |
2009年 | 3890篇 |
2008年 | 3149篇 |
2007年 | 2500篇 |
2006年 | 2210篇 |
2005年 | 1899篇 |
2004年 | 1723篇 |
2003年 | 1432篇 |
2002年 | 1280篇 |
2001年 | 1121篇 |
2000年 | 1062篇 |
1999年 | 945篇 |
1998年 | 544篇 |
1997年 | 472篇 |
1996年 | 475篇 |
1995年 | 441篇 |
1994年 | 425篇 |
1993年 | 285篇 |
1992年 | 463篇 |
1991年 | 347篇 |
1990年 | 365篇 |
1989年 | 327篇 |
1988年 | 226篇 |
1987年 | 215篇 |
1986年 | 189篇 |
1985年 | 166篇 |
1984年 | 134篇 |
1983年 | 113篇 |
1982年 | 93篇 |
1981年 | 71篇 |
1980年 | 51篇 |
1979年 | 87篇 |
1978年 | 61篇 |
1977年 | 60篇 |
1975年 | 61篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
T T Huang 《Plastic and reconstructive surgery》1990,86(2):275-280
The technique of placing the breast prosthesis beneath the pectoralis major and the serratus anterior muscles appears to minimize the incidence of the firm breast following breast reconstruction commonly seen with other techniques. However, in 8 of 146 individuals I have noted a problem with pain in the lateral aspect of the breast mound and the subscapular area, along with a depressed deformity superomedially and an unsightly bulge inferolaterally and/or laterally. Surgical exploration of the breast mound showed no abnormalities within the submuscular compartment. However, in all instances, the serratus anterior muscles were found to be detached from the ribcage all the way to the point beyond the posterior axillary line. While continuous pressure exerted on the serratus muscles by the implant appears to play an important role in the pathogenesis of this clinical entity, the onset of problems was usually delayed. Removal of the implants or repair of the cavity defects is necessary for patients who have developed this problem. 相似文献
52.
Rat embryo fibroblasts (REF52 cells) and the simian virus 40 transformed derivative (WT6 Ag6) were employed to characterize phospholipase D (PLD) activity in normal and transformed cells. In cells prelabeled with [3H]myristic acid or [3H]glycerol and treated with 12-O-tetradecanoylphorbol-13-acetate (TPA, 50 ng/ml medium) or vasopressin (VP, 100 ng/ml medium) in the presence of ethanol, the formation of labeled phosphatidylethanol (PEt) was 3- to 5-fold higher in REF52 cells than in the transformed cells. The transphosphatidylation of phosphatidylcholine (PC) to PEt was further examined in cell-free assay systems. Results demonstrated that the formation of PEt in the cell-free assays was dependent on the mode of substrate presentation and the source of the PC. With endogenous membrane-bound substrate, the formation of [3H]myristoyl-PEt was 5-fold higher in homogenates derived from normal cells as compared to transformed cell homogenates. In experiments using exogenous labeled PC isolated from either REF52 or transformed cells as substrate, cell-free PLD activity differed greatly with regard to the source of the PC. The formation of PEt from REF52-derived PC was approx. 4-fold higher as compared to PEt formed with PC derived from the transformed cells, irrespective of enzyme source. The results demonstrate that PLD in intact nontransformed fibroblasts is activatable by TPA and VP to a greater extent than in the transformed counterpart. The results from cell-free assays suggest that PLD activity is more dependent on the type of PC substrate than on the source of the enzyme. 相似文献
53.
A nonreductive community-level study of P availability was conducted using various forms of adsorbed P. Orthophosphate (Pi), inositol hexaphosphate (IHP), and glucose 6-phosphate (G6P) were adsorbed to a short-range ordered Al precipitate. These bound phosphates provided a P source sufficient to support the growth of microbial communities from acidic Brazilian soils (oxisols). Adsorbed IHP, the most abundant form of organic phosphate in most soils, had the lowest bioavailability among the three phosphates studied. Adsorbed G6P and Pi were almost equally available. The amount of adsorbed Pi (1 cmol P kg–1) required to support microbial growth was at least 30 times less than that of IHP (30 cmol P kg–1). With increased surface coverage, adsorbed IHP became more bioavailable. This availability was attributed to a change in the structure of surface complexes and presumably resulted from the decreased number of high-affinity surface sites remaining at high levels of coverage. It thus appears that the bioavailability of various forms of adsorbed phosphate was determined primarily by the stability of the phosphate-surface complexes that they formed, rather than by the total amount of phosphate adsorbed. IHP, having the potential to form stable multiple-ring complexes, had the highest surface affinity and the lowest bioavailability. Bioaggregates consisting of bacteria and Al precipitate were observed and may be necessary for effective release of adsorbed P. Bacteria in the genera Enterobacter and Pseudomonas were the predominate organisms selected during these P-limited enrichments.
Correspondence to: C. Shang 相似文献
54.
实验中观察到,用MUG培养基对植物药中的大肠杆菌定量时多发生荧光猝灭现象,影响检测结果。本文对此现象产生的原因与克服方法进行了系统的考察,发现以一种简便的转接方法可排除植物药介质对菌检的干扰。该方法由两组检验系列构成,当怀疑正常稀释系列(第一系列)40h培养液的荧光结果可能因猝灭现象呈假阴性时,立即分别将该系列的1—3号管培养液以0.5ml的接种量转接入新鲜的MUG培养基(第二系列),重新培养24h,荧光猝灭现象即可克服。综合两系列的荧光、产气和吲哚三项生化特征得出检品中大肠杆菌含量。实际应用表明,此法能显著提高使用该培养基时菌检结果的可靠性。 相似文献
55.
Bi(Ⅲ)与金属硫蛋白作用性质研究张保林,黄辉,朱凌燕,岳晟,唐雯霞(南京大学配位化学研究所,配位化学国家重点实验室,南京210093)如何降低顺铂或其它抗癌铂的毒性,一直是癌症化疗中的重要课题之一,最近研究发现预先给大鼠或肺癌病人服用铋盐,可以极大... 相似文献
56.
采用大鼠海马脑片体外缺血模型观察钙离子和蛋白激酶C(PKC)对神经元胞外谷氨酸(GLU)堆积的影响,结果显示:海马脑片在体外“缺血”10min,GLU在胞外的浓度增加4倍(从32±4升高到113±10pmol/(min.mgPr).n=6).N型钙通道拮抗剂蝙蝠葛苏林碱(DSL)或无钙培养液均能有效抑制这种浓度的升高(P<0.01).提示缺血10min引发的GLU浓度升高是受Ca2+内流调控的.当脑片在缺血状况下孵育30min,DSL只部分抑制这种GLU堆积,而无钙培养液则无影响,但这额外的GLU堆积可被PKC抑制剂H-7完全阻断,而被PKC激动剂PDB所加强;且不受钙调蛋白抑制剂Calmdazolium和8-溴-cAMP影响.提示缺血30min,胞外GLU的堆积受钙内流和PKC双重调控。 相似文献
57.
58.
The effects of salicylic acid (SA) on ethylene biosynthesis in detached rice leaves were investigated. SA at pH 3.5 effectively inhibited ethylene production within 2 h of its application. It inhibited the conversion of ACC to ethylene, but did not affect the levels of ACC and conjugated ACC. Thus, the inhibitory effect of SA resulted from the inhibition of both synthesis of ACC and the conversion of ACC to ethylene.Abbreviations ACC
1-aminocyclopropane-1-carboxylic acid
- EFE
ethylene-forming enzyme
- SA
salicylic acid 相似文献
59.
T. C. Pan T. H. Lin C. L. Tseng M. H. Yang C. W. Huang 《Biological trace element research》1993,39(2-3):117-128
Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological
study has implicated that high arsenic content in artesian well water of the endemic area, bears some important connection
with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination
in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls.
Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those
of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements
with the etiology of the disease is discussed. 相似文献
60.
莱氏衣原体膜上Mg~(2+)-ATPase用DOC溶解后,经Sepharose-6B和DEAE-CelluloseDE-52离子交换柱,得到了部分纯化的Mg~(2+)ATPase,并将此ATPase与不同极性头部的磷脂和膜糖脂重组,研究了不同的极性头部的磷脂和膜糖脂对ATPase活性的影响。此酶的活性不依赖酸性磷脂,PG、DPG、大豆磷脂等明显抑制酶活性,中性磷脂DMPC、PE、PC则能增加酶活性,其中尤以非双层脂PE的作用最为明显。从莱氏衣原体膜上提取的糖脂(MGDG,DGDG)单独和ATPase重组时,酶活性增加并不明显,当MGDG和DGDG以等比例混合时,能大大地增加酶活性。这表明Mg~(2+)-ATPase的活性很大程度上与磷脂的表面电荷及磷脂的组成相关。 相似文献