全文获取类型
收费全文 | 7533篇 |
免费 | 976篇 |
国内免费 | 1篇 |
出版年
2021年 | 95篇 |
2019年 | 66篇 |
2018年 | 80篇 |
2017年 | 75篇 |
2016年 | 110篇 |
2015年 | 187篇 |
2014年 | 202篇 |
2013年 | 273篇 |
2012年 | 325篇 |
2011年 | 325篇 |
2010年 | 238篇 |
2009年 | 184篇 |
2008年 | 315篇 |
2007年 | 264篇 |
2006年 | 275篇 |
2005年 | 224篇 |
2004年 | 251篇 |
2003年 | 253篇 |
2002年 | 220篇 |
2001年 | 222篇 |
2000年 | 208篇 |
1999年 | 184篇 |
1998年 | 121篇 |
1997年 | 102篇 |
1996年 | 106篇 |
1995年 | 101篇 |
1994年 | 92篇 |
1993年 | 90篇 |
1992年 | 145篇 |
1991年 | 185篇 |
1990年 | 197篇 |
1989年 | 141篇 |
1988年 | 149篇 |
1987年 | 153篇 |
1986年 | 148篇 |
1985年 | 134篇 |
1984年 | 118篇 |
1983年 | 105篇 |
1982年 | 96篇 |
1981年 | 107篇 |
1980年 | 99篇 |
1979年 | 121篇 |
1978年 | 112篇 |
1977年 | 88篇 |
1976年 | 72篇 |
1975年 | 70篇 |
1974年 | 100篇 |
1973年 | 96篇 |
1972年 | 83篇 |
1971年 | 79篇 |
排序方式: 共有8510条查询结果,搜索用时 31 毫秒
201.
High-pressure, high-temperature bioreactor for comparing effects of hyperbaric and hydrostatic pressure on bacterial growth. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We describe a high-pressure reactor system suitable for simultaneous hyperbaric and hydrostatic pressurization of bacterial cultures at elevated temperatures. For the deep-sea thermophile ES4, the growth rate at 500 atm (1 atm = 101.29 kPa) and 95 degrees C under hydrostatic pressure was ca. three times the growth rate under hyperbaric pressure and ca. 40% higher than the growth rate at 35 atm. 相似文献
202.
Upon treatment of Papaveracea cells with fungal elicitors, the biosynthesis of benzo[c]phenanthridine alkaloids is induced. Dihydrobenzophenanthridine oxidase, which catalyzes a later step in the biogenesis of these alkaloids, is one of the enzymes whose activity is elevated in the process. Here we report the 211-fold purification of the oxidase from elicited Sanguinaria canadensis by a combination of ammonium sulfate fractionation, DEAE-Sephadex, CM-Sephadex, Sephadex G-200, and either phenyl Superose or gel filtration chromatography. The purified enzyme utilized molecular oxygen to oxidize dihydrosanguinarine to sanguinarine with concomitant formation of hydrogen peroxide. A pH optimum of 7.0, Vmax of 27 nkat/mg protein, and apparent Km of 6.0 microM for dihydrosanguinarine were determined. Dihydrochelerythrine was also found to be a substrate for the purified enzyme, displaying an apparent Km of 10 microM. However, neither dihydronorsanguinarine nor the indole alkaloid ajmalicine was oxidized, indicating that the enzyme has some substrate specificity. Apparent molecular weight estimates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the most purified enzyme preparation obtained contained a major component of 77 kDa and two minor components between 59 and 67 kDa that can be associated with oxidase activity. Purified enzyme preparations possessed activity that was inhibited by sodium diethyldithiocarbamate, sodium azide, potassium cyanide, 1,4-DL-dithiothreitol, and mercaptoethanol. 相似文献
203.
204.
Long-term treatment of isolated rat soleus muscle with phorbol ester leads to loss of contraction-induced glucose transport. 总被引:2,自引:0,他引:2
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)
Muscle contraction involves mobilization of intracellular Ca2+ and is associated with several metabolic adjustments, including increased glucose transport. In the present study isolated rat soleus muscles were exposed to 12-O-tetradecanoylphorbol 13-acetate, and responses to both insulin and contraction in terms of glucose transport were assessed. Muscles treated with this phorbol ester for 12 h showed an increased basal rate of 3-O-methylglucose uptake, and responded partially to insulin but did not respond to contraction. Phorbol-ester-treated and non-treated (vehicle-only) muscles were indistinguishable in terms of pre-contraction content of adenine nucleotide, phosphocreatine, lactate and glycogen, as well as contractile performance and contraction-induced glycogenolysis. Phorbol ester treatment of isolated solei for 12 h resulted in the loss of 90% of protein kinase C activity as determined with histone IIIs as substrate, and 70% as determined by using phorbol ester binding. It is concluded that treatment of solei with phorbol ester gives rise to a marked loss of contraction-induced glucose transport. 相似文献
205.
We have extended the observations of previous transmission electron microscopy studies of sperm-egg fusion to include those of freeze-fracture replicas showing sperm-egg interactions before, during, and following sperm head fusion with the egg membrane. Hamster eggs were incubated with hamster sperm under polyspermic conditions and were observed after a period of 5-30 minutes. After fixation, the eggs and sperm were exposed to filipin, which binds beta-OH-sterols to form visible complexes in freeze-fracture replicas. Filipin can act as a marker for egg plasma membrane wherein it is abundant, while filipin is relatively scarce in the acrosome-reacted hamster sperm membrane, found only in the plasma membrane of the equatorial segment. The earliest sperm-egg interactions are observed between the egg microvilli and the perforatorium and the equatorial segment of the sperm, and the initial fusion between egg and sperm occurs in the vicinity of the equatorial segment. At later stages of fusion involving the postacrosomal segment, a clear line of demarcation is observed between the filipin-rich egg membrane and the filipin-poor sperm postacrosomal segment, suggesting that filipin binding lipids from the egg intercalate into the sperm membrane following membrane fusion. The anterior segment of the sperm does not fuse with the egg but is instead incorporated into a cytoplasmic vesicle derived from both sperm and egg membranes. In this latter step, filipin-sterol complexes are not found in sperm-derived membranes suggesting that there may be barriers to the movement of filipin binding lipids from the egg into these sperm membranes. 相似文献
206.
Summary A new culture method was used to study increases in wet and dry weight and soluble protein during normal development of the
transparent lens. Seven different media with more than ten different additives were tested for their effects on cultured lens
transparency.In vivo, rat lenses increased 53% in soluble protein content between 3 and 5.5 days of age. Only HL-1 serum-free medium containing
15 μg/ml insulin plus 1–2 ng/ml BB platelet-derived growth factor (PDGF), or 5–7 ng/ml epidermal growth factor (EGF) allowed
similar growthin vitro, during the same time period. Normal lens grwoth occurred in culture when fresh medium was delivered to lenses as a pulse
every 4–6 hours. Lenses decreased in dry weight and soluble protein content, and became opaque when the same medium was delivered
continuously. Lenses increased only 26% and 32% in soluble protein content when delivered pulses of HL-1 medium containing
BB PDGF or EGF in the absence of insulin. We suggest that pulsatile delivery of medium containing insulin and PDGF or EGF
stimulates lens growth during developmentin vitro. This pulsatile organ culture system is presented as a new approach for studying the effects of growth factors on cell proliferation,
differentiation, and receptor regulation in a developing tissue.
This work was supported by grants from EY-07031 and EY-04542 from the National Eye Institute and a grant from the Oculon Corporation.
Editor's statement This report documents an in vitro system that may mimic lens development and response to growth regulators
and hormones. The system may be useful for application to other organs and provide a foundation for cell and molecular level
analysis. 相似文献
207.
208.
Heterogeneity of the glutathione transferase genes encoding enzymes responsible for insecticide degradation in the housefly 总被引:6,自引:0,他引:6
Michael Syvanen Zonghan Zhou Jonathan Wharton Claire Goldsbury Alan Clark 《Journal of molecular evolution》1996,43(3):236-240
One of the four glutathione-S-transferases (GST) that is overproduced in the insecticide-resistant Cornell-R strain of the housefly (Musca domestica) produces an activity that degrades the insecticide dimethyl parathion and conjugates glutathione to lindane. In earlier
work, it was shown that the resistant Cornell-R carries an amplification, probably a duplication, of one or more of its GST
loci and that this amplification is directly related to resistance. Using polymerase chain reaction (PCR) amplification with
genomic DNA, multiple copies of the gene encoding the parathion-degrading activity (called MdGst-3) were subcloned from both
the ancestral, insecticide-susceptible strain BPM and from the insecticide-resistant Cornell-R. In BPM, three different MdGst-3
genes were identified while in Cornell-R, 12 different MdGst-3 sequences were found that, though closely related to ancestral
genes, had diverged by a few nucleotides. This diversity in MdGst-3 genomic sequences in Cornell-R is reflected in the expressed
sequences, as sampled through a cDNA bank. Population heterozygosity cannot account for these multiple GST genes. We suggest
that selection for resistance to insecticides has resulted in not only amplification of the MdGst-3 genes but also in the
divergence of sequence between the amplified copies.
Received: 22 November 1995 / Accepted: 23 February 1996 相似文献
209.
Inhibition of human immunodeficiency virus type 1 integrase by the Fab fragment of a specific monoclonal antibody suggests that different multimerization states are required for different enzymatic functions.
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
E V Barsov W E Huber J Marcotrigiano P K Clark A D Clark E Arnold S H Hughes 《Journal of virology》1996,70(7):4484-4494
We have characterized a murine monoclonal antibody (MAb 35), which was raised against human immunodeficiency virus type 1 (HIV-1) integration protein (IN), and the corresponding Fab 35. Although MAb 35 does not inhibit HIV-1 IN, Fab 35 does. MAb 35 (and Fab 35) binds to an epitope in the C-terminal region of HIV-1 IN. Fab 35 inhibits 3'-end processing, strand transfer, and disintegration; however, DNA binding is not affected. The available data suggest that Fab 35 inhibits enzymatic activities of IN by interfering with the ability of IN to form multimers that are enzymatically active. This implies that the C-terminal region of HIV-1 IN participates in interactions that are essential for the multimerization of IN. Titration of the various IN-mediated enzymatic activities suggests that different degrees of multimerization are required for different activities of HIV-1 IN. 相似文献
210.
Clark S. Monson 《Economic botany》1996,50(1):130-138
Mulberry trees in Northern Utah were located by historical references to local sericulture and by examining vegetation in proximity to pioneer-era two-story houses. It was usually in the upstairs bedrooms of these larger homes where silkworms were raised, and many of these houses planted one or two mulberry trees in their yards. Although mulberry planting and sericulture were once advocated by early Mormon leaders as a means to achieve economic self-sufficiency, ultimately this social and economic experiment failed, leaving relic mulberry groves dotted throughout Utah. Most of these groves have now disappeared in the wake of urban expansion. Preservation of a few relic trees is proposed as a means of preserving cultural ties to the past. 相似文献