全文获取类型
收费全文 | 432篇 |
免费 | 43篇 |
出版年
2021年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 18篇 |
2007年 | 9篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1995年 | 4篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1960年 | 4篇 |
1953年 | 3篇 |
1938年 | 4篇 |
1936年 | 9篇 |
1935年 | 5篇 |
1933年 | 8篇 |
1932年 | 9篇 |
1931年 | 9篇 |
1929年 | 7篇 |
1923年 | 3篇 |
1920年 | 2篇 |
1918年 | 3篇 |
1910年 | 2篇 |
排序方式: 共有475条查询结果,搜索用时 31 毫秒
1.
The primary structure of a procaryotic glycoprotein. Cloning and sequencing of the cell surface glycoprotein gene of halobacteria 总被引:40,自引:0,他引:40
The hexagonally patterned surface layer of halobacteria consists of a true glycoprotein. This procaryotic glycoprotein has recently been shown to exhibit novel features with respect to saccharide structure and saccharide biosynthesis. The primary structure and the location of glycosylation sites were determined by cloning and sequencing of the glycoprotein gene of Halobacterium halobium. According to the predicted amino acid sequence, the glycoprotein is synthesized with a N-terminal leader sequence of 34 amino acid residues reminiscent of eucaryotic and procaryotic signal peptides. A hydrophobic stretch of 21 amino acid residues at the C terminus probably serves as a transmembrane domain. 14 threonine residues are clustered adjacent to this membrane anchor and linked to these threonines are all the disaccharides of the cell surface glycoprotein. 12 N-glycosylation sites are distributed over the polypeptide chain. 相似文献
2.
Prompt chlorophyll a fluorescence kinetics at room temperature were measured from intact spruce needles. The fluorescence signal was recorded after varying light pretreatments. During the winter, induction curves showed characteristic changes in both the initial peak of fluorescence FV/FP (FP-FO/FP) and the steady state level Fdr (FP-FT/FP). Winter stress induced decreases in both values which showed close correlation to the light and temperature pre-history of the plants. In February changes in fluorescence induction indicative of a restoration of photosynthesis were detected and these corresponded to a rise of temperature above zero in combination with low light levels. In March increasing light intensity combined with chilling temperatures induced again decreases of both values of chlorophyll fluorescence induction suggesting the occurrence of photoinhibition. 相似文献
3.
Max Lechner Herbert Märkl Friedrich Götz 《Applied microbiology and biotechnology》1988,28(4-5):345-349
Summary In a newly constructed one-vessel dialysis fermentor, a strain of Staphylococcus carnosus TM300 carrying the lipase secretion plasmid pLipPS1 was used to investigate exoenzyme and biomass production. The bacterial culture grows in an inner compartment of 21 volume, separated from a 101 nutrient broth compartment by a conventional dialysis membrane. In order to avoid substrate depletion and to prolong the growth phase, a highly concentrated nutrient broth was used. The biomass production reached 60 g cell dry weight/l. The increase in extracellular lipase concentration was directly coupled with the increase of cell mass and reached a value of 230 mg/l culture supernatant. Harvesting the cells in the late growth phase, the lipase content was about 30% of the total exoproteins in the supernatant. 相似文献
4.
The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone 总被引:30,自引:1,他引:29 下载免费PDF全文
The basis of inhibition of photosynthesis by single acute O3 exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O3 for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO2 uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO2 uptake and the internal CO2 concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O3; no significant increase occurred for any of the other treatments. Analysis of the response of CO2 uptake to the internal CO2 concentration implied that the predominant factor responsible for the reduction in light-saturated CO2 uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O3, respectively. At saturating concentrations of CO2, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O3. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO2 uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O3, requiring 8 hours at 400 nanomoles per mole O3 before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO2 uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O3 fumigation. 相似文献
5.
R B Lechner N J Gurll D G Reynolds 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1985,178(2):227-233
The opiate antagonist naloxone increases arterial pressure, maximal left ventricular dp/dt and cardiac output when administered to dogs subjected to hemorrhagic shock. The purpose of this study was to investigate regional blood flow changes associated with naloxone treatment in anesthetized hypovolemic and normovolemic dogs. Hypovolemic dogs (n = 10) were bled over 30 min (t = -30 to t = 0) to a pressure of 45 mm Hg which was maintained for 1 hr. At t = 60, five dogs received naloxone (2 mg/kg + 2 mg/kg X hr), and five received an equal volume of saline. Regional blood flows were determined at t = -30, 45, and 90 min using 15-micron microspheres. Normovolemic dogs (n = 10) were subjected to the same protocol except they were not bled. During hypovolemia, naloxone produced significant increases in myocardial, intestinal, hepatic, and adrenal blood flows whereas saline treatment did not. No significant changes in skin, muscle, fat, pancreatic, renal, or brain flows were detected. The increases in blood flow were not associated with significant changes in vascular resistance. Naloxone had no significant effects on any hemodynamic parameter during normovolemia. The beneficial effects of naloxone in hemorrhagic shock include increased blood flow to vital organs due to increased perfusion pressure which is secondary to improved cardiac performance. 相似文献
6.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
7.
8.
Identification and purification of a family of dimeric major cold shock protein homologs from the psychrotrophic Bacillus cereus WSBC 10201. 总被引:2,自引:1,他引:1 下载免费PDF全文
Whole-cell protein patterns of a psychrotrophic Bacillus cereus strain from cultures grown at 7 and 30 degrees C were compared. This analysis revealed that at least three major proteins are expressed at a significantly higher rate at 7 degrees C than at 30 degrees C. The most abundant of these cold-induced proteins was a small polypeptide of 7.5 kDa, designated CspA, of B. cereus. In addition, four small proteins very similar in size to CspA were seen on both 7 degrees C and 30 degrees C two-dimensional protein gels. Immunoblot analysis using B. cereus anti-CspA antibodies indicated that the five proteins described above plus an additional sixth protein not visible on silver-stained two-dimensional gels are members of a B. cereus cold shock protein family. This hypothesis was corroborated by cloning and sequencing of the genes encoding five proteins of this family. The protein sequences deduced are highly similar and show homology to small procaryotic cold shock proteins and to the cold shock domain of eucaryotic Y-box proteins. Besides CspA, only one of the additional five CspA homologs was slightly cold inducible. In the presence of 100 mM NaCl, the two purified members of the protein family (CspA and CspE) elute as dimers at an apparent molecular mass of 15 kDa from a gel filtration column. At higher salt concentrations, they dissociate into their monomers. Their ability to bind to the ATTGG motif of single-stranded oligonucleotides was demonstrated by band shift analysis. 相似文献
9.
Steven A. Belinsky John F. Lechner Neil F. Johnson 《In vitro cellular & developmental biology. Animal》1995,31(5):361-366
Identifying the causal events and temporal aspects of lung cancer development requires the ability to isolate target and nontarget
cells for comparative analyses. Current methodology can either isolate only one pure specific cell population from a lung
or multiple cell types at lower purity. Previous studies in our laboratory have identified the alveolar type II cell as the
progenitor cell for tumor development in the A/J mouse. The purpose of this study was to develop new protocols for the isolation
and culture of type II and Clara cells from the mouse lung. Both type II and Clara cells were obtained in high purity using
a sequential centrifugal elutriation protocol. In the first elutriation, cell fractions were collected using a Standard chamber.
The type II and Clara cell fractions were then elutriated separately (two different separations) using a Sanderson chamber.
The final purity of the type II and Clara cell preparations was 73% and 76%, respectively. Colonies of 4 to 20 Clara cells
exhibiting epithelial morphology were evident 1 wk after plating in low serum medium. The growth of type II cells required
the addition of bronchioalveolar lavage fluid and acidic fibroblast growth factor to the medium. The isolation of viable mouse
type II and Clara cells in high purity should facilitate the identification of cell-specific changes in gene expressions or
in enzymatic pathways following in vivo or in vitro exposure to environmental carcinogens. 相似文献
10.
A zinc finger protein, essential for chromosome segregation, constitutes a putative DNA binding subunit of the Saccharomyces cerevisiae kinetochore complex, Cbf3. 总被引:12,自引:1,他引:11 下载免费PDF全文
J Lechner 《The EMBO journal》1994,13(21):5203-5211
A multisubunit protein complex, Cbf3, is a component of the Saccharomyces cerevisiae kinetochore. Cbf3 was recently shown to be essential for chromosome segregation in vivo and for movement of centromere DNA (CEN) along microtubules in vitro. Cbf3 contains three proteins, Cbf3a, Cbf3b and Cbf3c. Here the characterization of Cbf3b is described. Cbf3b contains an N-terminal Zn2Cys6 type zinc finger domain, a C-terminal acidic domain and a putative coiled coil dimerization domain. Cbf3b is essential for growth. Mutations within the zinc finger domain result in cells that exhibit a G2-M cell cycle delay and increased chromosome loss in each mitotic cell division. Therefore, Cbf3b has an essential function in chromosome segregation and the zinc finger domain executes part of this function presumably by providing the specific interaction between Cbf3 and CEN. Finally, data are provided to show that Cbf3c is encoded by CTF13, a gene that had been cloned recently by complementing a temperature sensitive mutant that exhibits chromosome loss as a result of a defective centromere. 相似文献