全文获取类型
收费全文 | 4267篇 |
免费 | 262篇 |
国内免费 | 1篇 |
出版年
2022年 | 16篇 |
2021年 | 37篇 |
2020年 | 24篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 44篇 |
2016年 | 72篇 |
2015年 | 121篇 |
2014年 | 151篇 |
2013年 | 270篇 |
2012年 | 245篇 |
2011年 | 247篇 |
2010年 | 150篇 |
2009年 | 167篇 |
2008年 | 237篇 |
2007年 | 255篇 |
2006年 | 248篇 |
2005年 | 234篇 |
2004年 | 240篇 |
2003年 | 262篇 |
2002年 | 303篇 |
2001年 | 100篇 |
2000年 | 80篇 |
1999年 | 79篇 |
1998年 | 49篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 40篇 |
1992年 | 74篇 |
1991年 | 42篇 |
1990年 | 42篇 |
1989年 | 40篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 36篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 25篇 |
1978年 | 13篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1973年 | 11篇 |
1971年 | 12篇 |
1970年 | 15篇 |
1966年 | 13篇 |
排序方式: 共有4530条查询结果,搜索用时 31 毫秒
61.
Hirobumi Suzuki Yasushi Sato Shizuo Fujiyama Nobuyoshi Ohba 《Biochemical genetics》1996,34(5-6):191-200
Japanese fireflies of the subfamily Luciolinae are biochemically analyzed using 13 allozymes, and the phylogenetic relationships obtained from this analysis are compared with their flash communication systems. As a result, the Japanese Luciolinae can be divided into three groups.Hotaria parvula andH. tsushimana together withLuciola yayeyamana andL. kuroiwae from the first group, and they use the same communication system.L. lateralis, Curtos okinawana, andC. costipennis make up the second group, and their communication systems are also the same.L. cruciata makes up the last one, and its communication system is different from the other fireflies of Luciolinae. Therefore, their taxonomical arrangement and communication systems are not congruent. However, the genetic similarity deduced by allozymic analysis of the members of the Japanese Luciolinae is highly consistent with their flash communication systems. 相似文献
62.
A smut fungus onPrimula sieboldii was newly found in Japan and identified asUrocystis tranzscheliana by comparative morphology. This species causes systemic infection ofP. sieboldii and produces sori in its ovaries.Contribution No. 121, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba. 相似文献
63.
Efficiency of serum copper/zinc ratio for differential diagnosis of patients with and without lung cancer 总被引:1,自引:0,他引:1
Tsunehiro Oyama Koji Matsuno Toshihiro Kawamoto Tetsuya Mitsudomi Takayuki Shirakusa Yasushi Kodama 《Biological trace element research》1994,42(2):115-127
We examined serum copper (Cu), serum zinc (Zn), and the serum copper/zinc ratio (Cu/Zn) in 162 patients. All of them were
seen to have an abnormal shadow in the chest X-ray films, that is, 109 patients with lung cancer (LC) and 53 patients with
no lung cancer (NLC). The mean Cu and Cu/Zn in LC patients were significantly higher than those in NLC patients (p<0.05). In LC patients, Cu and Cu/Zn were higher and Zn was lower in advanced tumors than early ones. There was a significantly
clear relation between Cu or Cu/Zn and the tumor (T) stages. When the relative risk (RR) of LC was estimated, it was seen
that the higher Cu and Cu/Zn became, the higher RR became. Furthermore, we showed the sensitivity of the receiver operator
characteristic of the test (ROC) curve for Cu, Cu/Zn, and carcinoembryonic antigen (CEA) to diagnose LC, as explained in a
paragraph of methods.The determinations of Cu, Zn, and Cu/Zn are simple and inexpensive. They also appear to have a great diagnostic value in determining the local invasion of LC and as a screening test in the
high-risk patients for LC. 相似文献
64.
Two β-galaclosidases (β-Galase-I and -II, EC 3.2.1.23) and two α-l -arabinofuranosidases (α-l -Arafase-I and -II. EC 3.2.1.55). were purified from mesophyll tissues of spinach (Spinacia oleracea L.), using chromatography on DEAE-cellulose, lactose-conjugated Sepharose CL-4B, and Sephadex G-100, or on hydroxylapatite and Sephadex G-150. The apparent molecular mass (Mr) of β-Galase-I and -II, respectively, were estimated to be 38 000 and 58 000 on SDS-PAGE and 64 000 and 60 000 on gel-permeation chromatography, indicating that the former was a dimeric protein. The isoelectric points of β-Galase-I and -II were 6.9 and 5.2, respectively. Both enzymes hydrolyzed maximally p-nitrophenyl (PNP) β-galactoside at pH 4.3, and were activated about 2-fold in the presence of BSA (100 μg ml?1). The activity of both enzymes was inhibited strongly by heavy metal ions and p-chloromercuriberszoate (p-CMB). d -Galactono-(1→4)-lactone and d -galactal served as potent competitive inhibitors for the enzymes. β-Galase-I and -II could be distinguished from each other in their relative rates and kinetic properties in the hydrolysis of aryl β-galactosides as well as of lactose and galacto-oligosaccharides. In particular. β-Galase-I exhibited a preferential exowise cleavage of β-1,6-galactotriose and β-1.3-galactan. α-l -Arafase-l (Mr 118000) and -II (M, 68 000) were optimally active on PNP α-l -arabinofuranoside at pH 4.8 and gave Km values of 1.2 and 2.2 mM. respectively. l -Arabino-(1 → 4)-lactone. Ag+, and SDS acted as inhibitors for the isozymes. α-l Arafase-I was characterized by its activity to hydrolyze PNP β-d -xylopyranoside besides PNP α-l -arabinofuranoside. inhibition by d -xylose and d -glucono-(1 → 5)-lactone. and less sensitivity to Hg2+. Cu2+, and p-CMB. Sugar beet arabinan was hydrolyzed rapidly by α-l Arafase-II at one-half the rate for PNP α-l arabinofuranoside, while the polysaccharide was less susceptible to α-l Arafase-I. A spinach leaf arabinogalactan-protein was practically resistant to the action of β-Galases, but its susceptibility to the enzymes increased remarkably after prior hydrolysis with α-l Arafase-Il. 相似文献
65.
Hayashi Takahisa; Takeda Takumi; Ogawa Kozo; Mitsuishi Yasushi 《Plant & cell physiology》1994,35(6):893-899
Xyloglucan oligosaccharides were isolated with various degreesof polymerization (DP) and reduced with tritiated sodium borohydride.The 3H-oligosaccharides were tested for their ability to bindto amorphous and microcrystalline celluloses and to cellulosefilter paper. The time course of binding indicated that theradiolabeled oligosaccharides continued to be bound for at least1 h after heating at 120°C. The binding probably requiredthe organization of the oligosaccharides and celluloses by gradualannealing after heating. Although neither pentasaccharide (glucose:xylose, 3 : 2), heptasaccharide (glucose: xylose, 4 : 3) andnonasaccharide (glucose : xylose : galactose : fucose, 4 : 3: 1 : 1) failed to bind to the celluloses, binding occurredwith oligosaccharides with DP equivalent to more than four consecutive1,4-ß-glucosyl residues. The extent of binding tothe celluloses increased gradually from octasaccharide (glucose:xylose, 5 : 3) to hendecosanosaccharide (glucose/xylose, 12: 9), with the increase in the DP of 1,4-ß-glucosylresidues. The binding of reduced cello-dextrins to celluloserequired at least 4 consecutive 1,4-ß-glucosyl residues.The extent of binding of cellopentitol or cellohexitol to cellulosewas similar to that of hendecosanosaccharide, showing lowerbinding for xyloglucan oligosaccharides in spite of longer chainsof 1,4-ß-glucosyl residues. These findings suggestthat the mode of binding to cellulose of xyloglucan oligosaccharidesis different from that of cello-oligosaccharides. (Received February 18, 1994; Accepted June 1, 1994) 相似文献
66.
Yasuko Nagatsuka Shigemasa Hanazawa Yasuyuki Koroiwa Tamotsu Fukuda Toshio Suganuma Yasushi Ono 《Letters in applied microbiology》1994,19(4):206-209
We have established 950 and 430 oligoclonal B-lymphoblastoid cell lines (LCL) from two normal persons and eight autoimmune disease patients, respectively by using Epstein-Barr virus (EBV)-induced transformation. To re-evaluate the EBV technique for production of human monoclonal antibodies (mAb) related to infectious disease, we screened these oligoclonal LCLs for antibodies against 31 bacterial strains systematically. A total of 74 cultures out of 1380 were reactive to a total of 18 strains out of 31. Among these, eight cultures showed 10-3 antibody (Ab) titers to Pseudomonas aeruginosa serotypes C, E, F and I, Staphylococcus aureus, Serratia marcescens and Bacillus cereus. Ten cultures showed 10-2 Ab titers to Ps. aeruginosa serotypes D, E, F and I, Ps. maltophilia, Staph, epidermidis, Klebsiella ozaenae, Ser. marcescens and B. subtilis. The results reveal the further possibilities for the EBV technique to produce various infectious disease-related human mAbs. 相似文献
67.
68.
Cloning, nucleotide sequence and expression of a hemolysin gene of Clostridium septicum 总被引:4,自引:0,他引:4
Abstract A genomic library of Clostridium septicum NCTC547 strain was made in Escherichia coli by means of λgt10. The DNA insert of a hemolysin-positive (Hly+ ) λ-clone was transferred into pUC19. The resulting plasmid, pCS21, confers a Hly+ phenotype on E. coli . Crude lysates of E. coli (pCS21) possessed a strong lytic activity on human erythrocytes and also a lethal effect on mice, characteristic of an α toxin. Nucleotide sequence analysis revealed that the insert DNA (5.2 kb) in pCS21 included at least one open reading frame of 1380 bp. The coding frame for hemolysin was predicted to be 1329 bp in size and to encode a protein of 49.8 kDa. It coincided with the molecular mass (48 kDa) of the α toxin secreted by C. septicum . Taken together, the data indicated that plasmid pCS21 indeed encoded an α toxin gene of C. septicum . 相似文献
69.
Mohammad B. Rashid Katsuhiko Shirahige Naotake Ogasawara Hiroshi Yoshikawa 《Gene》1994,150(2):213-220
We have analyzed the relationship between autonomously replicating sequence (ARS) structure and function for three ARS (ARS605, ARS607 and ARS609) from chromosome VI of Saccharomyces cerevisiae by systematic XhoI-linker mutation in the ARS consensus sequence (ACS) and flanking sequences. All mutations that encroached upon the ACS destroyed ARS activity. DNA sequences stimulative for ARS function were identified on either side of the ACS of ARS605 and only on the 3'-side of the ACS of ARS607. In ARS609, however, no such stimulative sequences were observed. Base substitutions complementary to the wild-type sequence of those stimulative regions, in ARS605 and ARS607, that did not change the AG of unwinding nor affected ARS activity suggests that these regions have, at least, a function as DNA-unwinding elements (DUE). ARS605, ARS607 and ARS609 DNA are of low AG value and showed hypersensitivity to single-strand-specific nuclease when inserted in negatively supercoiled plasmid. Linker mutations inhibitory for ARS activity (5L11 and 7L14) also caused significant changes in local nucleotide (nt) sensitivity within the ACS and its adjoining regions. Complementary base substitutions, however, did not affect these changes in local nt sensitivity. These results imply that the stimulative regions flanking the ACS are necessary to produce an optimum conformation around the ACS which may be important for full ARS activity. 相似文献
70.
Stable isotopic structure of aquatic ecosystems 总被引:1,自引:0,他引:1
Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous
function and structure of an ecosystem. Distributions ofδ
13C andδ
15N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope
biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic
framework of the ecosystem was successfully described in aδ
15N–δ
13C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived
organic matter, and marine-derived organic matter.
A trophic-level effect of15N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived
organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin.
The contributions of both land and marine organic matter were comparable for mollusca in the lagoon. 相似文献