全文获取类型
收费全文 | 41881篇 |
免费 | 15905篇 |
国内免费 | 6篇 |
专业分类
57792篇 |
出版年
2022年 | 178篇 |
2021年 | 567篇 |
2020年 | 2339篇 |
2019年 | 3899篇 |
2018年 | 4209篇 |
2017年 | 4429篇 |
2016年 | 4545篇 |
2015年 | 4409篇 |
2014年 | 4180篇 |
2013年 | 4840篇 |
2012年 | 2436篇 |
2011年 | 2272篇 |
2010年 | 3503篇 |
2009年 | 2119篇 |
2008年 | 1215篇 |
2007年 | 880篇 |
2006年 | 919篇 |
2005年 | 867篇 |
2004年 | 757篇 |
2003年 | 800篇 |
2002年 | 710篇 |
2001年 | 645篇 |
2000年 | 512篇 |
1999年 | 374篇 |
1998年 | 136篇 |
1992年 | 243篇 |
1991年 | 231篇 |
1990年 | 188篇 |
1989年 | 220篇 |
1988年 | 237篇 |
1987年 | 248篇 |
1986年 | 222篇 |
1985年 | 256篇 |
1984年 | 207篇 |
1983年 | 170篇 |
1979年 | 245篇 |
1978年 | 164篇 |
1977年 | 145篇 |
1976年 | 140篇 |
1975年 | 171篇 |
1974年 | 266篇 |
1973年 | 265篇 |
1972年 | 253篇 |
1971年 | 242篇 |
1970年 | 255篇 |
1969年 | 246篇 |
1968年 | 188篇 |
1967年 | 186篇 |
1966年 | 168篇 |
1965年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A fluorometric methods is described for determination of cardiac and urinary 3-methoxytyramine, a metabolite of dopamine. Methoxy metabolites were isolated on Amberlite CG-50 resin and oxidation to emitter form was performed with K3Fe(CN)6. Good specificity and sensitivity of determination, and a high recovery of 3-MT were obtained. 相似文献
62.
63.
64.
65.
66.
For three types of self-sucking impellers (fourand six-pipe and disk impellers) mixing power, initial point, amount of gas leaving the impeller and mass transfer coefficient were determined experimentally. Investigations were performed for two systems: water and biomass solution.From the point of view of a minimum mixing power and maximum mass transfer coefficient the best impeller has been chosen. Fuzzy multiobjective optimization for determination of optimum operating conditions is proposed.List of Symbols
c
concentration of oxygen
-
D
tank diameter
-
d
impeller diameter
-
g
acceleration of gravity
-
H
height of liquid in the tank
-
H
height of liquid above impeller, H=H-y
-
k
consistency coefficient
-
k
L
a
volumetric mass transfer coefficient
-
N
rotational speed of impeller
-
n
flow behaviour index
-
P
mixing power for pure liquid
-
P
G
mixing power for aerated liquid
-
V
G
volumetric air flow rate
-
y
distance of impeller from the tank bottom
-
v
a
apparent kinematic viscosity of liquid
-
density of liquid
-
time
-
gas hold-up
- Eu=P/N
3
d
5
or EuG=P
G
/N
3
d
5
Euler Number for non-gassed or aerated liquid
- Fr=N
2
d/g
Froude Number
- Fr*=N
2
d
2
/g(H -y)
modified Froude Number
- KG=V
G
/N d
3
gas flow number
- Re=N d
2
/v
a
Reynolds Number
- Sh=k
K
a/(g
2
/v
a
)1/3
Sherwood Number 相似文献
67.
B. Bilińska 《Histochemistry and cell biology》1989,93(1):105-110
Summary Effect of LH, vinblastine and cytochalasin B on the cytoskeleton of cultured Leydig cells was investigated using monoclonal antibodies and fluorescence microscopy. After LH addition and treatment with cytoskeletal disrupting drugs, three main effects were observed: 1) increase of androgen level secreted by cultured mouse Leydig cells, 2) changes of cell-shape towards regular and rounded, 3) increase of 5,3-HSD activity. The results are discussed in respect to possible involvement of cytoskeleton in the regulation of steroidogenesis. 相似文献
68.
I Grys M Dudziak W Piechota W Rózański M Su?ek M Adamczyk-Szymańska 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1990,45(49-50):984-986
The study involved 126 patients with cholelithiasis. Set of biochemical, radiological, endoscopic, and ultrasound examinations was carried out in these patients. Potential coincidence of clinical symptoms and causes of so-called postcholecystectomy syndrome was the purpose of a 1-year follow-up studies. The significance of the results are discussed. 相似文献
69.
J Leowski A Czech P Lastowiecki K Jaskó?a J Tatoń 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1990,45(1-3):30-35
Monotherapy of hypertension with acebutolol in diabetics in daily dose of 200-400 mg for 6 weeks induced only non-significant and practically not acceptable hypotensive effect in groups of patients with hypertension and diabetes type I or type II without nephropathy. No therapeutical effect was observed in hypertension in diabetics type I with nephropathy. Administration of acebutolol to hypertensive diabetic patients with nephropathy resulted in tendency to increase in albuminuria. Values of creatinine clearance did not change at the same time. Also no effect of acebutolol on glycemic or lipid indices was observed. The lack of clear hypotensive effect under studied conditions of acebutolol in diabetic patients contrasted with its significant action in comparative group of hypertensive non-diabetic subjects. 相似文献
70.
Unusual organization of the tropharium in the telotrophic ovarioles of an insect, Saldula saltatoria
The tropharium of the common shorebug Saldula saltatoria consists of 2 zones: the apical mitotic region and the distal one comprising numerous mononucleate nurse cells. Each individual nurse cell is connected to the centrally located trophic core by a thin cytoplasmic projection referred to as a trophic process. The accumulations of a dense material interpreted as the remnants of intercellular bridge rim are observed associated with the trophic process membrane. In the light of these results the establishment of telotrophic ovarioles in hemipterans is discussed. 相似文献