全文获取类型
收费全文 | 3358篇 |
免费 | 272篇 |
国内免费 | 3篇 |
出版年
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 49篇 |
2015年 | 84篇 |
2014年 | 93篇 |
2013年 | 142篇 |
2012年 | 156篇 |
2011年 | 164篇 |
2010年 | 100篇 |
2009年 | 115篇 |
2008年 | 140篇 |
2007年 | 161篇 |
2006年 | 166篇 |
2005年 | 150篇 |
2004年 | 130篇 |
2003年 | 133篇 |
2002年 | 128篇 |
2001年 | 59篇 |
2000年 | 58篇 |
1999年 | 52篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 44篇 |
1995年 | 36篇 |
1994年 | 45篇 |
1993年 | 35篇 |
1992年 | 41篇 |
1991年 | 47篇 |
1990年 | 30篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 28篇 |
1980年 | 41篇 |
1977年 | 30篇 |
1975年 | 22篇 |
1974年 | 25篇 |
1973年 | 20篇 |
1970年 | 17篇 |
1968年 | 20篇 |
1936年 | 17篇 |
1932年 | 18篇 |
排序方式: 共有3633条查询结果,搜索用时 15 毫秒
101.
Ernst Weber Evangelos Papamokos Wolfram Bode Robert Huber Ikunoshin Kato Michael Laskowski 《Journal of molecular biology》1981,149(1):109-123
The third domain of Japanese quail ovomucoid, a Kazal type inhibitor, has been crystallized and its crystal structure determined at 2.5 Å resolution using multiple isomorphous replacement techniques. The asymmetric unit contains four molecules. In the crystal the molecules are arranged in two slightly different octamers with approximate D4 symmetry. The molecules are held together mainly by interactions of the N-terminal residues, which form a novel secondary structural element, a β-channel.The molecule is globular with approximate dimensions 35 Å × 27 Å × 19 Å. The secondary structural elements are a double-stranded anti-parallel β-sheet of residues Pro22 to Gly32 and an α-helix from Asn33 to Ser44. The reactive site Lys18-Asp19 is located in an exposed loop. It is close to Asn33 at the N terminus of the helical segment. The polypeptide chain folding of ovomucoid bears some resemblance to other inhibitors in the existence of an anti-parallel double strand following the reactive site loop. 相似文献
102.
Danny M. Gee Gary M. Hathaway Richard H. Palmieri Ernst A. Noltmann 《Journal of molecular biology》1980,142(1):29-42
As a corollary to X-ray crystallographic work performed by H. Muirhead, detailed studies on crystalline pig muscle phosphoglucose isomerase have been conducted to establish its basic physical and chemical properties. The enzyme species being investigated by X-ray diffraction has been determined to be isoenzyme III. Its molecular weight in the native state was found to be 132,000, its s020,w value to be 7·25 S. The enzyme is composed of two subunits of equal molecular weight (66,000). Its amino acid composition is largely similar to that of rabbit muscle phosphoglucose isomerase, with the significant exception that the pig muscle isomerase contains only three sulfhydryl groups per polypeptide chain (two of them accessible to titration with p-mercuribenzoate) as compared with twice that number for the rabbit muscle enzyme. This low number of sulfhydryl groups is interpreted as being responsible for the ease with which heavy-atom, isomorphous derivatives could be prepared for the pig muscle enzyme by Shaw & Muirhead (1977). 相似文献
103.
Edward Ernst 《BMJ (Clinical research ed.)》1980,281(6250):1280-1281
104.
Anders
lund Hans Kindahl Ernst Oliw ke Lindgren Jan Bertil Larsson 《Prostaglandins & other lipid mediators》1980,19(5):791-803
Abortion or delivery were induced by extra-amniotic instillation of Rivanol during the second trimester in twelve patients and during the third trimester in two patients with fetal death and one patient with fetal acrania. Serial sampling of amniotic fluid was performed through a transabdominal catheter and the levels of free arachidonic acid (AA), prostaglandin F2α (PGF2α), prostaglandin E2 (PGE2), 6-keto-prostaglandin F1α (6-keto-PGF1α) and thromboxane B2 (TXB2) were determined. The levels of AA, PGF2α, PGE2, 6-keto-PGF1α and TXB2 in amniotic fluid increased significantly during induction with the exception of AA in fetal death which was high and remained constant during induction. Furthermore, PGF2α, 6-keto-PGF1α and TXB2 were all significantly correlated to AA.These observations suggested that free AA is released during Rivanol-induction of abortion and labour giving an increased synthesis of PGF2α, PGE2 prostacyclin and thromboxane A2 in the fetal membranes and the decidua but not in the fetus. This increase might be relevant for the initiation and progress of abortion and labour in these patients. 相似文献
105.
PGI2 and 6-keto-PGF1α were converted to 6-methoxime-PGF1α (6-MeON-PGF1α) by treatment with methoxyamine HCl in acetate buffer. The formed 6-MeON-PGF1α was measured by radioimmunoassay. Antisera were raised in rabbits after immunization against 6-MeON-PGF1α-BSA conjugate. Diluted 1:20.000 to bind 50% of the tracer (3H-6-MeON-PGF1α, 100 Ci/mmol), the antiserum cross reacted 0.8% with PGE2, 1% with PGF2α and less than 0.2% with PGD2, PGF1α, PGF2β and TXB2. The radioimmunoassay was used to estimate release of PGI2 and 6-keto-PGF1α from chopped rabbit renal medulla and cortex incubated in Krebs-Ringer bicarbonate buffer (37°C, 30 min). The 6-keto-PGf1α radioimmunoassay was validated in biological samples by mass fragmentography. The chopped medulla (n=5) released 38±9 ng/g/min and the cortex (n=5) 4.7±2.0 ng/g/min, while the release of immunoreactive PGE2 (iPGE2) and iPGF2α was 171±26 and 74±13 ng/g/min from the medulla and 4.3±1.3 and 2.7±0.3 ng/g/min from the cortex, respectively. The results confirm previous findings, which indicate that in the renal medulla prostaglandin endoperoxides are mainly transformed to prostaglandins, while in the cortex transformation to PGI2 seems to be of greater
importance. 相似文献
106.
Kupffer cells were isolated from pronase-perfused rat livers and were maintained as a monolayer culture in a state of high purity and viability. Immediately after contact with zymosan particles, O2 uptake of the Kupffer cells increased fivefold; about 50% of the net oxygen consumed was accounted for as superoxide released into the medium. Concomitantly, a transient burst of luminol-dependent chemiluminescence, an increased activity of NAD(P)H oxidase and a stimulation of the flow of glucose through the hexose monophosphate shunt were observed. Chemiluminescence and O2- production were almost completely inhibited by superoxide dismutase and iodoacetate. Zymosan-induced chemiluminescence was not inhibited in the presence of the non-penetrating thiol reagents, 5,5'-dithio-bis-2-nitrobenzoate and iodoacetyl-sepharose. Iodoacetate acted on the cytosolic glucose-6-phosphate dehydrogenase rather than on NAD(P)H oxidase of the cell membrane. 相似文献
107.
108.
Response of Guanosine 5′-Triphosphate Concentration to Nutritional Changes and Its Significance for Bacillus subtilis Sporulation 总被引:4,自引:4,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have investigated the changes in the guanosine 5'-triphosphate (GTP) and P-ribosyl-PP pools in stringent and relaxed strains of Bacillus subtilis under conditions frequently used to initiate sporulation. After a shift-down from a Casamino Acids-glutamate to a glutamate medium (Sterlini-Mandelstam shift-down), the pools of adenosine 5'-triphosphate and P-ribosyl-PP increased in both strains; in the stringent strain, ppGpp and pppGpp increased and GTP decreased rapidly, whereas in the relaxed strain, ppGpp and pppGpp increased only slightly and GTP decreased only slowly and less extensively. The stringent strain sporulated well, whereas the relaxed strain sporulated late and poorly. Addition of decoyinine, an inhibitor of guanosine 5'-monophosphate synthetase, caused a further decrease of GTP and initiated good sporulation of the relaxed strain. After a shift-down from a glucose-lactate to a lactate medium (Ramaley-Burden shift-down) the pool of P-ribosyl-PP (and GTP) decreased in both strains, indicating a shortage of purine precursors. This shift-down also caused a stringent response which prevented the consumption of nucleotides, as shown by the maintenance of adenosine 5'-triphosphate at a high concentration in the stringent strain but not in the relaxed strain. After a delay, the relaxed strain, in which GTP decreased as fast as in the stringent strain, sporulated also as efficiently. In nutrient sporulation medium the stringent strain and, less effectively, the relaxed strain accumulated ppGpp and pppGpp transiently towards the end of exponential growth. Eventually, the P-ribosyl-PP pool decreased drastically in both strains. In all cases the initiation of sporulation was correlated with a significant decrease of GTP. Granaticin, an antibiotic which prevents the charging of leucyl-transfer ribonucleic acid, was used to show that the stringent response inhibited the formation of xanthosine monophosphate from inosine monophosphate. It prevented the accumulation of xanthosine monophosphate in decoyinine-treated cultures of the stringent strain but not in those of the relaxed strain. 相似文献
109.
The proteins and glycoproteins of human blood platelets and platelet membranes in both the reduced and the unreduced states have been analysed by isoelectric focusing and sodium dodecyl sulphate-discontinuous polyacrylamide gel electrophoresis in a two-dimensional technique. Gels which had been stained with periodic acid-Schiff's reagent could be counter-stained with Coomassie Brilliant Blue, simplifying the recognition of components which stain with both reagents. The major glycoproteins and some of the proteins have been identified and the characteristics of the membrane and of the whole platelet components established in this system. 相似文献
110.