全文获取类型
收费全文 | 7307篇 |
免费 | 388篇 |
国内免费 | 6篇 |
出版年
2023年 | 11篇 |
2022年 | 49篇 |
2021年 | 75篇 |
2020年 | 59篇 |
2019年 | 56篇 |
2018年 | 90篇 |
2017年 | 74篇 |
2016年 | 163篇 |
2015年 | 241篇 |
2014年 | 242篇 |
2013年 | 539篇 |
2012年 | 463篇 |
2011年 | 500篇 |
2010年 | 303篇 |
2009年 | 280篇 |
2008年 | 484篇 |
2007年 | 510篇 |
2006年 | 463篇 |
2005年 | 451篇 |
2004年 | 514篇 |
2003年 | 395篇 |
2002年 | 410篇 |
2001年 | 76篇 |
2000年 | 74篇 |
1999年 | 84篇 |
1998年 | 104篇 |
1997年 | 83篇 |
1996年 | 74篇 |
1995年 | 78篇 |
1994年 | 63篇 |
1993年 | 57篇 |
1992年 | 63篇 |
1991年 | 54篇 |
1990年 | 55篇 |
1989年 | 51篇 |
1988年 | 52篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1981年 | 29篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 24篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有7701条查询结果,搜索用时 156 毫秒
61.
The natural 13C abundance (13C value) of the field-grown leguminousplants (soybean, kidney bean, pea, azuki bean, mung bean, peanutand cowpea) was investigated by mass spectrometry with a precisionbetter than %0.2 for 13C. Among organs of premature plants,the leaves had the most negative values, and the nodules generallyhad the least negative values, and other organs, fruits, stemsand roots, showed intermediate values. In the soybeans so farinvestigated, the grains of nodulating plants exhibited higher13C values than nonnodulating lines. The 13C values of the grainsvaried depending on the species: peanuts showed the most negativevalues. Possible causes underlying these variations are discussed.
3Institute of Biological Sciences, University of Tsukuba, Sakura-mura,Ibaraki 305, Japan. (Received December 3, 1982; Accepted May 25, 1983) 相似文献
62.
Interindividual distance and influence of dominance on feeding in a natural Japanese macaque troop 总被引:5,自引:0,他引:5
Takeshi Furuichi 《Primates; journal of primatology》1983,24(4):445-455
In a natural troop of Japanese macaques (Macaca fuscata yakui), the dominant-subordinate relationship restricted the feeding behavior of the subordinate in two ways: (1) the dominant
drives away the subordinate through agonistic interactions; and (2) the subordinate avoids approaching the dominant without
any agonistic interactions. These occurred only infrequently, and only when an interindividual distance was less than a certain
distance, which is called the “tolerance/intolerance” (T/I) distance. On the other hand, the usual interindividual distance
when feeding was much greater than the T/I distance. Therefore dominance has little influence on feeding in the study troop.
In the study troop, the T/I distance between kin-related females was shorter than that between unrelated individuals. Although
this difference may facilitate kin selection if the troop faces severe competition over concentrated food, the difference
does not seem to influence survival or reproductive rate in the study troop. 相似文献
63.
Two adenosine 3',5'-cyclic monophosphate (AMP)-deficient mutants of Vibrio cholerae (biotype El Tor) were successfully isolated by nitrosoguanidine treatment followed by pencillin screening for pleiotropic sugar-negative clones. Exogenous cyclic AMP is required for the fermentation of sucrose, trehalose, fructose, maltose, and mannose but not of glucose, as well as for the formation of normal flagella and specific somatic antigens. A striking characteristic of the mutants is their growth behavior at higher temperatures. They cannot grow on TCBS selective plates at 37 C or higher unless they are provided with a supply of exogenous cyclic AMP, although they are capable of producing colonies on the same medium, even without cyclic AMP, at temperatures lower than 30 C. Since the mutants are converted to spheroplasts, spindle forms, and spiral filaments in cyclic AMP-free media at 37 C, and this phenomenon is stopped by the addition of cyclic AMP or a combination of 20% sucrose and 0.2% magnesium chloride, it is assumed that cyclic AMP is essential for the synthesis of the cell wall of V. cholerae at higher temperatures. 相似文献
64.
Mutants of Group D1Salmonella Carrying the Somatic Antigen of Group A Organisms: Isolation and Serological Characterization 总被引:2,自引:2,他引:0
O antigen mutants were obtained from Salmonella durban, a group D(1) organism, by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Serological studies demonstrated that the mutants lost the O-9 antigen factor of the parent organism but acquired the O-2 factor specific to group A Salmonella. Lipopolysaccharides of the mutant strains contained paratose which determines the specificity of O-2 factor. Tyvelose, present in the wild-type lipopolysaccharide, was not found in the mutants. H antigens and other biological characteristics of the mutant strains were the same as those of the wild-type organism. The present finding implies that group A Salmonella species might be derived from group D(1) organisms. 相似文献
65.
An investigation was made on the factors influencing the acetic acid concentration in the culture liquid of the aerobic fermentations where acetie acid was used as a carbon source. The acetic acid concentration in the culture liquid changed in proportion to the amount of unutilizable acid or base supplied. This was explained by the principle of conservation of electroneutrality. Another factor affecting the acetic acid concentration in the culture liquid was bicarbonate ions which were formed by the dissolution and dissociation of carbon dioxide in the gas phase of the fermentor. The increment in bicarbonate ion concentration was equal to the decrement in the acetie acid concentration in the culture liquid. 相似文献
66.
67.
Isolated microspores of Chinese cabbage (Brassica campestris ssp. pekinensis) were incubated in modified NN medium containing 10% sucrose in darkness at 33°C for one day followed by culture at 25°C. After 14 days of culture, microspores developed into embryos ranging from globular to cotyledonary stage. Plants were regenerated after transfer of embryos to medium containing 3% sucrose and no plant growth regulators.Abbreviations NN
Nitsch and Nitsch
- MS
Murashige and Skoog
- NAA
naphthaleneacetic acid
- BA
6-benzylaminopurine 相似文献
68.
Noriaki Inamura Saburo Sone Akio Okubo Eiji Kunishige Mie Nakanishi Takeshi Ogura 《Cancer immunology, immunotherapy : CII》1989,28(3):164-170
Summary Human blood monocytes were isolated by counter-flow centrifugal elutriation from healthy donors and these noncytotoxic monocytes were rendered tumoricidal to allogeneic melanoma (A375) cells by activation with a synthetic acyltripeptide (FK-565), as assessed by measuring release of [125I]iododeoxyuridine in 72 h. When monocytes were treated with FK-565 for 16 h, and then fixed with paraformaldehyde, they showed cytotoxicity to A375 melanoma cells. The fixed-monocyte-mediated cytotoxicity to A375 cells was induced by the synergistic actions of FK-565 and recombinant interferon- (rIFN-), but not other cytokines [rIFN-A, rIFN-, tumor necrosis factor (TNF), interleukin (IL)-2, -3 and -6]. For synergistic activation of monocytes with induction of a membrane-associated antitumor monokine, the monocytes had to be incubated first with rIFN- and then with FK-565. FK-565 also acted synergistically with rIFN- to stimulate monocytes to produce membrane-associated IL-1 activity, which induced C3H/HeJ thymocyte blastogenesis in response to phytohemagglutinin P. The tumoricidal and thymocytestimulating activities of the fixed monocytes were almost completely inhibited by a specific anti-(IL-1) antiserum, but not by a specific anti-(IL-1) antiserum or monoclonal anti-TNF antibody. These results suggest that membrane-associated IL-1 of human blood monocytes can be induced by two activation signals (rIFN- then FK-565) at their suboptimal concentrations.Abbreviations IL
interleukin
- IFN
interferon
- TNF
tumor necrosis factor 相似文献
69.
Tadao Niijima Takashi Umeda Manabu Kuriyama Hiroyuki Ohmori Yohsuke Matsumura Tomoyasu Tsushima Toyoko Tanahashi Jun Yoshimoto Toshihiko Asahi Norimasa Ike Taiichiro Johsen Noritaka Ishido Naoki Mitsuhata Takeshi Uyama Hiroyoshi Tanaka Hideo Ueda Jisaburo Sakatoku Norio Yamamoto Kazuo Nagata Yukitoshi Fujita Masaaki Morioka Kazuo Kurokawa Susumu Kagawa Tomoyuki Ishibe Yasutoshi Himeno Toyofumi Ueda 《Cancer immunology, immunotherapy : CII》1989,30(2):81-85
Summary In order to examine its clinical efficacy, recombinant human interferon- (rIFN-) was instilled intravesically into 51 patients with superficial bladder cancer. Ten patients, who received intermittent intravesical instillation at a dose of (3–36) × 106 U rIFN- on days 1–3 every week, showed no response. Thirty-two patients received intravesical instillation at a dose of (3–36) × 106 U every day for 10–20 days. Eight patients showed partial response, indicating an efficacy rate of 25%. Nine patients received divided doses of 18 × 106 U twice a day every day for 10–20 days. Six patients showed partial response, indicating an efficacy rate of 67%. This value was significantly higher than that obtained by administering divided doses. The response to intravesical instillation therapy with rIFN- varies with treatment protocol. Frequent and longer exposure to rIFN- may induce better regression of superficial bladder cancer. Six incidences of side-effects were found in five cases (9.8%): pollakiuria in one, pain on micturition in two, fever in two, and eruption in one case. All of these side-effects were slight and reversible after drug withdrawal. Laboratory tests showed only a few changes with low severity. Thus, rIFN- is potentially a new drug for instillation therapy of superficial bladder cancer, in view of the absence of adverse effects. 相似文献
70.
Nucleotide sequence of the gene for cholesterol oxidase from a Streptomyces sp. 总被引:9,自引:3,他引:6
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)
The nucleotide sequence of a 2.1-kilobase-pair fragment containing the Streptomyces choA gene, which codes a secreted cholesterol oxidase, was determined. A single open reading frame encodes a mature cholesterol oxidase of 504 amino acids, with a calculated Mr of 54,913. The leader peptides extend over 42 amino acids and have the characteristics of a signal sequence, including basic amino acids near the amino terminus and a hydrophobic core near the signal cleavage site. Analyses of the total amino acid composition and amino acid sequencing of the first 21 amino acids from the N terminus of the purified extracellular enzyme agree with the values deduced from nucleotide sequencing data. 相似文献