全文获取类型
收费全文 | 11048篇 |
免费 | 677篇 |
国内免费 | 316篇 |
专业分类
耳鼻咽喉 | 30篇 |
儿科学 | 74篇 |
妇产科学 | 47篇 |
基础医学 | 1252篇 |
口腔科学 | 98篇 |
临床医学 | 697篇 |
内科学 | 1342篇 |
皮肤病学 | 111篇 |
神经病学 | 650篇 |
特种医学 | 259篇 |
外国民族医学 | 1篇 |
外科学 | 305篇 |
综合类 | 1208篇 |
一般理论 | 1篇 |
预防医学 | 481篇 |
眼科学 | 217篇 |
药学 | 4736篇 |
中国医学 | 283篇 |
肿瘤学 | 249篇 |
出版年
2023年 | 109篇 |
2022年 | 246篇 |
2021年 | 334篇 |
2020年 | 249篇 |
2019年 | 251篇 |
2018年 | 218篇 |
2017年 | 223篇 |
2016年 | 243篇 |
2015年 | 298篇 |
2014年 | 401篇 |
2013年 | 602篇 |
2012年 | 425篇 |
2011年 | 519篇 |
2010年 | 430篇 |
2009年 | 364篇 |
2008年 | 396篇 |
2007年 | 396篇 |
2006年 | 455篇 |
2005年 | 425篇 |
2004年 | 379篇 |
2003年 | 363篇 |
2002年 | 320篇 |
2001年 | 271篇 |
2000年 | 250篇 |
1999年 | 226篇 |
1998年 | 216篇 |
1997年 | 196篇 |
1996年 | 172篇 |
1995年 | 190篇 |
1994年 | 226篇 |
1993年 | 176篇 |
1992年 | 202篇 |
1991年 | 202篇 |
1990年 | 195篇 |
1989年 | 181篇 |
1988年 | 178篇 |
1987年 | 152篇 |
1986年 | 132篇 |
1985年 | 162篇 |
1984年 | 148篇 |
1983年 | 94篇 |
1982年 | 161篇 |
1981年 | 128篇 |
1980年 | 134篇 |
1979年 | 96篇 |
1978年 | 83篇 |
1977年 | 64篇 |
1976年 | 46篇 |
1975年 | 24篇 |
1974年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
11.
稳定性核素测定大鼠小肠蛋白质合成 总被引:2,自引:1,他引:1
目的:建立稳定性核素([L-^15N]亮氨酸)测定大鼠小肠蛋白质合成率的方法。方法:分别测定静脉注射相同剂量[L-^15N]亮氨酸不同时相的大鼠小肠^15N丰度及不同剂量[L-^15N]亮氨酸同一时相的大鼠小肠^15N丰度。结果:大鼠小肠游离氨基酸池中^15N核素丰度在注射后0.5h内呈线性上升并达高峰,维持4h后缓慢下降,小肠蛋白质中的^15N丰度0.5h至12h基本维持不变;随着注射剂量的增加,大鼠小肠蛋白质分数合成率(FSR)亦增加,当[L-^15N]亮氨酸剂量在1.0mmol/kg以上,FSR并不随施加[L15N]亮氨酸剂量的加大而增加。结论:在进行大鼠小肠蛋白质合成率测定时,一次性静脉注射的测量最佳时限为0.5h,剂量为1.0mmol/kg。 相似文献
12.
介绍国内外近年来报道的新型经皮渗透促进剂的研究与开发进展,重点介绍若干具代表性的新合成的化合物以及新发现的天然产物,包括内酰胺类、糖苷类、氨基酸衍生物、聚合物、挥发油和酶类等,为合成和发现更加安全、高效的促渗剂提供线索. 相似文献
13.
14.
S. Bereswill F. Fassbinder C. Völzing A. Covacci R. Haas M. Kist 《Medical microbiology and immunology》1998,186(4):177-187
Various strains of Helicobacter pylori were able to lyse erythrocytes from sheep, horse, and human when grown on blood agar. The hemolysis did not depend on the
production of the vacuolating cytotoxin VacA as demonstrated by the hemolytic behavior of an isogenic vacA-negative mutant strain. The hemolytic activity could be detected in cell-free supernatants and was not regulated by iron.
To isolate genes coding for proteins involved in the destruction of erythrocytes, a plasmid-based DNA library was screened
for expression of lytic activity on blood agar. This approach revealed that the H. pylori ribA gene confers hemolytic properties to Escherichia coli. The ribA gene encodes the enzyme GTP-cyclohydrolase II [EC 3.5.4.25] that catalyzes the initial step in the synthesis of riboflavin.
The predicted amino acid sequence of the H. pylori RibA protein showed a high degree of similarity to equivalent enzymes from microorganisms and from plants. The single gene
on a plasmid restored riboflavin synthesis in a ribA mutant of E. coli and induced hemolytic activity. Furthermore, ribA overexpression was associated with the production of a fluorescent yellow molecule that was not identical with riboflavin.
Hemolysis was also seen for the ribA gene from E. coli, indicating that this feature was not specific for the H. pylori gene. The presence of ribA in various H. pylori strains was confirmed by Southern blot hybridization and by polymerase chain reaction with specific primers. This analysis
revealed that microdiversity exists within the DNA region upstream from ribA, which was further confirmed by nucleotide sequence analysis.
Received: 25 July 1997 相似文献
15.
16.
RACHEL PHILOSOF-OPPENHEIMER ISRAEL PECHT MATI FRIDKIN 《Chemical biology & drug design》1995,45(2):116-121
The facile thiolytic cleavage of the O-2,4-dinitrophenyl (Dnp) tyrosine bond was applied to the solid-phase synthesis of the 22-amino acid residue peptide H-Asp-Ala-Val-Tyr -Thr-Gly-Leu-Asn-Thr-Arg-Asn-Gln-Glu-Thr-Tyr -Glu-Thr-Leu-Lys-His-Glu-Lys-OH, corresponding to positions 62-83 in the chain of the type 1 receptor for Fcε, domains expressed on the rat mucosal-type mast cells (line RBL-2H3). A method for the spectrophotometric determination of insoluble O-Dnp as well as of unprotected phenolic moieties of tyrosine was developed. It is based on monitoring S-Dnp-2-mercaptoethanol, produced upon O-Dnp thiolysis by 2-mercaptoethanol. © Munksgaard 1995. Dedicated to the memory of Dr. Susumu Funakoshi, a dear friend and a leader in peptide chemistry. 相似文献
17.
R. Alan Aitken Michael C. Bibby John A. Double Andrea L. Laws Robert B. Ritchie David W. J. Wilson 《Archiv der Pharmazie》1997,330(7):215-224
A range of 18 derivatives of flavone-8-acetic acid (FAA) with substituents on the 2-phenyl group have been prepared and their anti-tumour activity evaluated in vitro against a panel of human and murine tumour cell lines and in vivo against MAC 15A. There was no clear-cut relationship between in vitro and in vivo activity but the activity in each situation was found to be very sensitive to the precise substitution pattern with closely related isomers giving widely different activities. Some of the compounds, notably 10b,cj , and r , were active in vivo and these require further studies in order to evaluate their potential for development. 相似文献
18.
羟基胆烷酸类衍生物的抗癌活性研究Ⅰ.3β,5α,6β-三羟基胆烷-24-酸及其衍生物的合成与体外抗癌活性 总被引:3,自引:0,他引:3
报道3β,5α,6β三羟基胆烷24酸及其衍生物的合成及对小鼠L1210白血病细胞的体外抗癌活性.实验表明3β,5α,6β三羟基胆烷24酸,3β,5α,6β三羟基胆烷24酸甲酯及3β,6β二乙酰氧基5α羟基胆烷24酸甲酯有较好的抗癌活性 相似文献
19.
Quality and standardization in blood component preparation with an automated blood processing technique 总被引:3,自引:0,他引:3
van Rhenen Vermeij de Voogt Bernes & Payrat 《Transfusion medicine (Oxford, England)》1998,8(4):319-324
The use of automated blood processors in combination with bottom and top blood containers has been found to improve the standardization and quality of blood components. A study was performed to validate a new type of processor (Optipress® II) and compare its performance with a first generation processor (Optipress® I).
Primary separation on the Optipress II was investigated on 570 mL (± 10%) of anticoagulated blood in a nonpaired study. In addition, the quality of the products in routine production was compared between the results of the Optipress I and Optipress II. The whole blood units were kept overnight at room temperature (20 ± 2 °C). Separation was performed under conditions to obtain 55 mL buffy coats with a 50% haematocrit (ht). Platelet concentrate preparation was investigated in a paired study and compared to the routine manual method using PAS II additive solution. Parameters studied were volume, red cell, white cell and platelet counts, ht, haemoglobin (hb, total and free).
Primary separation was more efficient in the Optipress II because the platelet count was lower in the erythrocyte concentrates ( P < 0.0001), platelets were lower in plasma ( P < 0.0001) and platelet counts were higher in buffy coats ( P < 0.0001). Buffy coat volume showed less variation (Optipress II VC = 4%, Optipress I VC = 7.4%). Secondary separation did not show differences between the Optipress II and manual method but was advantageous because of the automatic termination of the procedure.
Further improvement of standardization in blood component preparation is possible with an automated blood processor, leading to improvement of the quality of blood products for patient care. 相似文献
Primary separation on the Optipress II was investigated on 570 mL (± 10%) of anticoagulated blood in a nonpaired study. In addition, the quality of the products in routine production was compared between the results of the Optipress I and Optipress II. The whole blood units were kept overnight at room temperature (20 ± 2 °C). Separation was performed under conditions to obtain 55 mL buffy coats with a 50% haematocrit (ht). Platelet concentrate preparation was investigated in a paired study and compared to the routine manual method using PAS II additive solution. Parameters studied were volume, red cell, white cell and platelet counts, ht, haemoglobin (hb, total and free).
Primary separation was more efficient in the Optipress II because the platelet count was lower in the erythrocyte concentrates ( P < 0.0001), platelets were lower in plasma ( P < 0.0001) and platelet counts were higher in buffy coats ( P < 0.0001). Buffy coat volume showed less variation (Optipress II VC = 4%, Optipress I VC = 7.4%). Secondary separation did not show differences between the Optipress II and manual method but was advantageous because of the automatic termination of the procedure.
Further improvement of standardization in blood component preparation is possible with an automated blood processor, leading to improvement of the quality of blood products for patient care. 相似文献
20.
以环己酮为起始原料,经与苯肼缩合、氧化、Mannich 反应制得1,2,3,9-四氢-3-二甲胺基甲基-4H-咔唑-4-酮盐酸盐(5),后者再与2-甲基咪唑缩合、甲基化合成翁丹西隆,总收率为10.4%。 相似文献