全文获取类型
收费全文 | 4345篇 |
免费 | 328篇 |
国内免费 | 3篇 |
出版年
2022年 | 34篇 |
2021年 | 47篇 |
2020年 | 48篇 |
2019年 | 56篇 |
2018年 | 83篇 |
2017年 | 71篇 |
2016年 | 72篇 |
2015年 | 111篇 |
2014年 | 172篇 |
2013年 | 249篇 |
2012年 | 260篇 |
2011年 | 301篇 |
2010年 | 184篇 |
2009年 | 142篇 |
2008年 | 172篇 |
2007年 | 213篇 |
2006年 | 196篇 |
2005年 | 158篇 |
2004年 | 149篇 |
2003年 | 136篇 |
2002年 | 114篇 |
2001年 | 126篇 |
2000年 | 131篇 |
1999年 | 106篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 49篇 |
1995年 | 42篇 |
1994年 | 35篇 |
1993年 | 34篇 |
1992年 | 74篇 |
1991年 | 90篇 |
1990年 | 88篇 |
1989年 | 84篇 |
1988年 | 44篇 |
1987年 | 63篇 |
1986年 | 70篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 44篇 |
1982年 | 48篇 |
1981年 | 35篇 |
1980年 | 25篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 32篇 |
1976年 | 24篇 |
1975年 | 21篇 |
1974年 | 23篇 |
1972年 | 26篇 |
排序方式: 共有4676条查询结果,搜索用时 17 毫秒
71.
Differential Agar Medium for Separating Streptococcus lactis and Streptococcus cremoris 总被引:5,自引:4,他引:1 下载免费PDF全文
M. Srinivasulu Reddy E. R. Vedamuthu C. J. Washam G. W. Reinbold 《Applied microbiology》1969,18(5):755-759
Lomofungin is a new antimicrobial agent obtained from the culture broth of Streptomyces lomondensis sp. n. UC-5022. Lomofungin is an acidic, olive-yellow, crystalline compound which inhibits, in vitro, a variety of pathogenic fungi, yeasts, and gram-positive and gram-negative bacteria. 相似文献
72.
73.
74.
Respiratory sinus arrhythmia in the denervated human heart 总被引:8,自引:0,他引:8
Bernardi L.; Keller F.; Sanders M.; Reddy P. S.; Griffith B.; Meno F.; Pinsky M. R. 《Journal of applied physiology》1989,67(4):1447-1455
We performed this study to test whether the denervated human heart has the ability to manifest respiratory sinus arrhythmia (RSA). With the use of a highly sensitive spectral analysis technique (cross correlation) to define beat-to-beat coupling between respiratory frequency and heart rate period (R-R) and hence RSA, we compared the effects of patterned breathing at defined respiratory frequency and tidal volumes (VT), Valsalva and Mueller maneuvers, single deep breaths, and unpatterned spontaneous breathing on RSA in 12 normal volunteers and 8 cardiac allograft transplant recipients. In normal subjects R-R changes closely followed changes in respiratory frequency (P less than 0.001) but were little affected by changes in VT. On the R-R spectrum, an oscillation peak synchronous with respiration was found in heart transplant patients. However, the average magnitude of the respiration-related oscillations was 1.7-7.9% that seen in normal subjects and was proportionally more influenced by changes in VT. Changes in R-R induced by Valsalva and Mueller maneuvers were 3.8 and 4.9% of those seen in normal subjects, respectively, whereas changes in R-R induced by single deep breaths were 14.3% of those seen in normal subjects. The magnitude of RSA was not related to time since the heart transplantation, neither was it related to patient age or sex. Thus the heart has the intrinsic ability to vary heart rate in synchrony with ventilation, consistent with the hypothesis that changes, or rate of changes, in myocardial wall stretch might alter intrinsic heart rate independent of autonomic tone. 相似文献
75.
A Karasik S S Reddy R B Pepinsky T Brock C R Kahn 《Journal of cellular physiology》1990,142(2):231-235
Epidermal growth factor (EGF) may either stimulate or inhibit cell growth. To elucidate the mechanism of these varied effects, we compared EGF action in parental A431 cells in which cell growth is inhibited, and clone 15, a mutant of these cells resistant to EGF growth inhibition. In both lines, EGF receptor was present in similar concentrations and underwent tyrosine phosphorylation to the same extent. Likewise, in both lines, acute exposure to EGF stimulated an increase in free cytoplasmic [Ca2+], as well as a similar increase in phosphorylation of lipocortin 1, a major substrate for the EGF receptor kinase whose phosphorylation is calcium-dependent. On the other hand, pretreatment of clone 15 cells with EGF for 72 h abolished EGF-induced phosphorylation of lipocortin 1 and led to a loss of the increase in cytoplasmic free [Ca2+], whereas no such desensitization was seen in the parental A431 cells. These data indicate a link between EGF-induced increase in cytoplasmic calcium, lipocortin phosphorylation, and cell growth and suggest that differences in mechanisms of desensitization to these immediate actions of EGF may lead to altered growth response to this hormone. 相似文献
76.
Decay accelerating factor (DAF) is a glycophospholipid-anchored membrane glycoprotein that protects mammalian host cells from inadvertant complement lysis. The effects of inhibiting mucin-type O-glycosylation on the cell surface expression of DAF were studied by introducing an expression vector for human DAF into wild-type Chinese hamster ovary and ldlD cells. The ldlD cells express reversible defects in the addition of galactose and N-acetylgalactosamine (GalNAc) to oligosaccharide chains on glycoproteins and glycolipids. Mucin-type O-glycosylation of proteins is inhibited in ldlD cells and can be selectively corrected by the addition of GalNAc to the culture medium. The attachment of a phosphatidylinositol phospholipase C-sensitive glycolipid anchor to DAF and its efficient sorting to the cell surface in ldlD cells were independent of galactose and GalNAc additions to glycolipids and proteins. Attachment of galactose and GalNAc to DAF's glycolipid anchor were apparently not required for its normal function. However, in the absence of O-glycosylation DAF was proteolytically cleaved soon after reaching the cell surface, and a large fragment of DAF was released into the culture medium. This rapid proteolysis/release resulted in the expression of very low steady state levels of O-glycosylation-deficient DAF as measured by immunoblotting. These results, in conjunction with those obtained from studies of three other membrane glycoproteins expressed in ldlD cells, suggest that O-linked sugars on membrane glycoproteins may frequently play a role in determining the level of cell surface expression of these proteins. 相似文献
77.
Beneficial interaction between photosynthesis and respiration in mesophyll protoplasts of pea during short light-dark cycles 总被引:1,自引:0,他引:1
The respiratory uptake or photosynthetic evolution of oxygen by mesophyll protoplasts of pea ( Pisum sativum L. cv. Arkel) were monitored during successive short. (3–5 min) cycles of darkness and illumination. The rate of respiration was nearly doubled after 3–4 short periods of illumination while there was a 15–20% enhancement in photosynthesis with cycles of illumination and darkness preceding illumination. Such interaction between photosynthesis and respiration was statistically significant when bicarbonate was present in the reaction medium. The inhibitors of photosynthesis [3(3,4–dichlorophenyl)-l,l-dimethylurea (DCMU), glyceraldehyde] decreased respiration after periods of illumination, whereas inhibitors of respiratory electron transport (Rotenone, antimycin A, NaN3 ) suppressed photosynthesis, as well. We suggest that a rapid beneficial interaction exists between photosynthesis and respiration in protoplasts, even during short cycles of light and darkness. 相似文献
78.
Changes in the cell surface of vaginal epithelial cells were studied by scanning microscopy and fluorescence spectroscopy. Microvilli which are prominent features of the vaginal epithelial cells in proestrus and diestrus are replaced by sheet-like structures in the estrus phase. Surface morphology of vaginal epithelial cells of estradiol primed rat resembles the vaginal cells from estrus phase rats whereas vaginal cells from control rats resembles the diestrus phase. Measurement of the fluidity of the membranes indicated that the vaginal epithelial cell membrane of estrus rats is more fluid compared to proestrus and diestrus. Similarly, estradiol primed immature rat vaginal epithelial cell membrane was observed to be more fluid than the corresponding control. 相似文献
79.
Determination of the respiration kinetics for mycelial pellets of Phanerochaete chrysosporium. 总被引:2,自引:2,他引:0 下载免费PDF全文
In mycelial pellet cultures of the white rot basidiomycete Phanerochaete chrysosporium, low oxygen concentration negatively affects the production of the extracellular lignin peroxidases and manganese peroxidases which are key components of the lignin-degrading system of this organism. To test the hypothesis that oxygen limitation in the pellets is responsible for this effect, oxygen microelectrodes were used to determine oxygen concentration gradients within the mycelial pellets of P. chrysosporium. Pellets were removed from oxygenated cultures, allowed to equilibrate with air, and probed with oxygen microelectrodes. The oxygen profiles were modelled assuming that O2 uptake follows a Michaelis-Menten relationship. The Vmax and Km values for oxygen uptake were 0.76 +/- 0.10 g/m3 of pellet per s and 0.5 +/- 0.3 g/m3, respectively. These kinetic values were used to predict respiration rates in air-flushed cultures, oxygen-flushed cultures, and cultures with large pellets (diameter greater than 6 mm). The predicted respiration rates were independently validated by experimentally measuring the evolution of carbon dioxide from whole cultures. 相似文献
80.
We report the use of a sensitive and specific enyzme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) to study the expression of protein D, a major androgen-regulated sperm-binding glycoprotein at the protein and mRNA level in different anatomical regions of the rat epididymis. The concentration of protein D in the caput, corpus and cauda region of the epididymis was 10.2 +/- 0.67, 7.3 +/- 0.61 and 22.8 +/- 1.34 ng/micrograms total protein, respectively. The total RNA extracted from the caput, corpus and cauda regions of the rat epididymis was amplified by PCR with oligonucleotide primers specific for the 5' and 3' portion of protein D cDNA. Compared to the caput and cauda region, a significant reduction (greater than 82 +/- 3%) in the expression of protein D mRNA levels was observed for corpus epididymal RNA. This data demonstrates regional differences in the concentration of protein D and suggests that protein D expression may be regulated at the level of mRNA within the corpus epididymidis. 相似文献