全文获取类型
收费全文 | 13356篇 |
免费 | 1130篇 |
国内免费 | 7篇 |
出版年
2022年 | 78篇 |
2021年 | 149篇 |
2020年 | 107篇 |
2019年 | 119篇 |
2018年 | 161篇 |
2017年 | 135篇 |
2016年 | 229篇 |
2015年 | 446篇 |
2014年 | 470篇 |
2013年 | 685篇 |
2012年 | 799篇 |
2011年 | 784篇 |
2010年 | 565篇 |
2009年 | 469篇 |
2008年 | 723篇 |
2007年 | 687篇 |
2006年 | 666篇 |
2005年 | 656篇 |
2004年 | 653篇 |
2003年 | 642篇 |
2002年 | 541篇 |
2001年 | 198篇 |
2000年 | 226篇 |
1999年 | 219篇 |
1998年 | 198篇 |
1997年 | 135篇 |
1996年 | 157篇 |
1995年 | 142篇 |
1994年 | 124篇 |
1993年 | 150篇 |
1992年 | 178篇 |
1991年 | 151篇 |
1990年 | 152篇 |
1989年 | 131篇 |
1988年 | 147篇 |
1987年 | 124篇 |
1986年 | 93篇 |
1985年 | 133篇 |
1984年 | 152篇 |
1983年 | 133篇 |
1982年 | 136篇 |
1981年 | 125篇 |
1980年 | 129篇 |
1979年 | 109篇 |
1978年 | 123篇 |
1977年 | 120篇 |
1976年 | 92篇 |
1975年 | 99篇 |
1974年 | 105篇 |
1973年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Donald A. Bryant Robert de Lorimier Gerard Guglielmi S. Edward Stevens Jr 《Archives of microbiology》1990,153(6):550-560
The phycobilisomes and phycobiliproteins of Synechococcus sp. PCC 7002 wild-type strain PR6000 have been isolated and characterized. The hemidiscoidal phycobilisomes of strain PR6000 are composed of eleven different polypeptides: phycocyanin and subunits; allophycocyanin and subunits; subunit of allophycocyanin B; the allophycocyanin -subunit-like polypeptide of Mr 18 000; the linker phycobiliprotein of Mr 99 000; and non-chromophore-carrying linker polypeptides of Mr 33 000, 29 000, 9000, and 8000. Several of these polypeptides were purified to homogeneity and their amino acid compositions and amino-terminal amino acid sequences were determined. Analyses of the phycobiliproteins of Synechococcus sp. PCC 7002 were greatly facilitated by comparative studies performed with a mutant strain, PR6008, constructed to be devoid of the phycocyanin and subunits by recombinant DNA techniques and transformation of strain PR6000. The absence of phycocyanin did not greatly affect the allophycocyanin content of the mutant strain but caused the doubling time to increase 2–7-fold depending upon the light intensity at which the cells were grown. Although intact phycobilisome cores could not be isolated from this mutant, it is probable that functionally intact cores do exist in vivo.Abbreviations used SDS-PAGE
polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate
- 2D-PAGE
two-dimensional gel electrophoresis in which the first dimension consisted of isoelectric focusing in the presence of 8.0 M urea in the pH range 4–6 and the second dimension consisted of electrophoresis in the presence of sodium dodecylsulfate. The nomenclature employed for the phycobiliprotein subunits and linker polypeptides is that defined by Glazer (1985) 相似文献
92.
93.
Roger V. Lebo Lee A. Anderson Salvatore DiMauro Eric Lynch Peter Hwang Robert Fletterick 《Human genetics》1990,86(1):17-24
Summary When probes throughout the McArdle disease (myophosphorylase) gene region were used to search for DNA polymorphisms, only an MspI polymorphism was found in 94 enzyme-probe combinations. Along with an insertion/deletion polymorphism more 3 to the gene locus, these polymorphisms will be informative in 75% of at-risk patients. These results contrast strikingly to the six polymorphic sites detected in 15 enzyme-probe combinations in the homologous Her's disease (liver phosphorylase) gene region. This single MspI polymorphic site includes a CpG sequence of known increased mutability suggesting that DNA regions with rare polymorphisms will have most polymorphic sites at sequences with enhanced mutability. Fluorescence in situ hybridization sublocalized this gene to proximal band 11q13, establishing a point of cross-reference between the physical and genetic maps. 相似文献
94.
95.
96.
97.
One hundred and twenty eight British and Irish nephrologists were questioned about their policy for HIV testing of patients with end stage renal failure being considered for renal replacement therapy. A total of 101 (79%) replied. In the case of candidates for dialysis roughly one third of respondents tested only people they considered at risk of infection with HIV and nearly one fifth considered testing unnecessary. In the case of candidates for transplantation routine HIV testing was carried out by 68 of 100 nephrologists; 22 tested only patients "at risk" and 10 did not test. A positive HIV test result was considered by most but not all respondents (63/86) to exclude patients from transplantation. Twenty four of 88 nephrologists considered that HIV positivity should exclude patients from haemodialysis, but only seven of 87 would exclude such patients from peritoneal dialysis. Similar attitudes pertained for patients with end stage renal failure who refused HIV testing. Testing with the patient''s knowledge and consent was the policy of two thirds of nephrologists, but a patient''s signature was obtained by only 24 of 88. There should be a consensus on practice for HIV testing of patients with end stage renal failure. 相似文献
98.
Aberrant regulation of the metabolism of the insulin receptor in Swarm rat chondrosarcoma chondrocytes.
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Treatment of Swarm rat chondrosarcoma chondrocytes for 3 days in media containing either non-recombinant pig or recombinant human insulin (1 micrograms/ml) increased the rate of proteoglycan synthesis approximately 6-fold compared with cells cultured in the absence of insulin. The concentrations of human and pig insulin that stimulated the cells to double their rate of proteoglycan synthesis were approximately 1 ng/ml and approximately 2 ng/ml respectively. Because physiological concentrations of insulin do not influence proteoglycan synthesis in non-transformed chondrocytes, the findings indicated a possible abnormality in the insulin-dependent regulation of the insulin receptor in these tumour cells. Like most cells, chondrosarcoma chondrocytes down-regulated their insulin receptors when incubated with insulin for 30 min. However, the number of plasma-membrane and intracellular insulin receptors did not decrease when the chondrocytes were exposed to insulin chronically for 4 days. Chondrocytes were cultured in media containing 2H-, 13C- and 15N-labelled amino acids, and the heavy-isotope density-shift method was used to investigate both the rate of degradation and the rate of synthesis of the insulin receptor. Although the rate of synthesis of the receptor was slightly faster in the insulin-treated cultures, as assessed by a slightly faster rate of appearance of the 'heavy' receptor, the rate of degradation of the receptor was slower in the insulin-treated cultures. The half-lives for the 'light' receptors were approx. 18 h and 10 h for chondrocytes cultured in insulin-containing and insulin-free media respectively. These studies in vitro indicate that the apparent up-regulation of insulin receptors that occurs in this transformed cell upon long-term exposure to insulin is primarily the result of a decreased rate of receptor degradation. 相似文献
99.
Prof. Dr. Dick R. Nässel Mats H. Holmqvist Roger C. Hardie Rolf Håkanson Frank Sundler 《Cell and tissue research》1988,253(3):639-646
Summary Antibodies to histamine were used for immunocytochemical studies of the visual system in the flies Calliphora erythrocephala and Musca domestica. Specific immunolabeling of photoreceptors was found both in the compound eyes and ocelli of both species. In the compound eyes histamine-like immunoreactivity (HA-IR) was found in all the short visual fibers (photoreceptors R1–6) and one type of long visual fiber (photoreceptor R8). In addition, the ocellar photoreceptors also show HA-IR. In view of earlier biochemical and pharmacological/physiological findings by Elias and Evans (1983) and Hardie (1987) it thus seems likely that histamine is a neurotransmitter in insect photoreceptors. Interestingly, the second type of long visual fiber (photoreceptor R7) has recently been found to be GABA-immunoreactive (Datum et al. 1986). The two types of long visual fibers may hence use different transmitters which act on different receptors of the postsynaptic neurons in the second visual neuropil, the medulla. In addition to the photoreceptors in the retina and ocelli, we found processes of HA-IR neurons in one of the optic lobe neuropils, the lobula. This finding indicates that histamine may also be a transmitter in certain interneurons in the visual system.Abbreviations
HA
histamine
-
GABA
-amino butyric acid
-
GAD
glutamic acid decarboxylase
-
5-HT
5-hydroxytryptamine (serotonin)
-
HA-IR
histamine-like immunoreactivity
-
R1-R6
class of short-axoned photoreceptors
-
R7 and R8
long-axoned photoreceptors
-
LMC
large monopolar neuron of lamina
-
HSA
human serum albumin
-
PBS
phosphate-buffered saline
-
DEPC
diethylpyrocarbonate 相似文献
100.
William J. Kraemer Lawrence E. Armstrong Roger W. Hubbard Louis J. Marchitelli Natalie Leva Paul B. Rock Joseph E. Dziados 《European journal of applied physiology and occupational physiology》1988,57(4):399-403
No data exists regarding responses of human atrial natriuretic factor (ANF) to exercise in the heat. The purpose of this study was to examine the responses of plasma ANF to high intensity submaximal (71% +/- 0.9 VO2max) exercise in the heat over an eight day acclimation period. Fourteen healthy males volunteered to participate in the study. Subjects performed intermittent exercises on a treadmill (0% grade) during 50 min of each 100 min trial in an environmental chamber maintained at 41.2 +/- 0.5 degrees C, 39.0 +/- 1.7% relative humidity. Blood was obtained from an antecubital vein after standing 20 min in the heat prior to exercise, and immediately after exercise. Measures were compared on days 1, 4 and 8. ANF did not change pre- to post-exercise nor did it change over the eight day heat acclimation period despite other heat acclimation adaptations. Conversely, plasma aldosterone (ALDO), renin activity (PRA) and cortisol (COR) all increased (p less than 0.05) pre- to post-exercise on each day but again no changes were observed over the eight day period. These data support that ANF may not increase when ALDO and PRA increases are observed. 相似文献