全文获取类型
收费全文 | 5081篇 |
免费 | 488篇 |
国内免费 | 1篇 |
专业分类
5570篇 |
出版年
2022年 | 30篇 |
2021年 | 53篇 |
2020年 | 35篇 |
2019年 | 44篇 |
2018年 | 41篇 |
2017年 | 47篇 |
2016年 | 98篇 |
2015年 | 169篇 |
2014年 | 165篇 |
2013年 | 239篇 |
2012年 | 312篇 |
2011年 | 354篇 |
2010年 | 218篇 |
2009年 | 196篇 |
2008年 | 274篇 |
2007年 | 331篇 |
2006年 | 295篇 |
2005年 | 318篇 |
2004年 | 319篇 |
2003年 | 292篇 |
2002年 | 322篇 |
2001年 | 63篇 |
2000年 | 44篇 |
1999年 | 84篇 |
1998年 | 81篇 |
1997年 | 68篇 |
1996年 | 60篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 57篇 |
1992年 | 51篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 41篇 |
1986年 | 36篇 |
1985年 | 33篇 |
1984年 | 49篇 |
1983年 | 39篇 |
1982年 | 43篇 |
1981年 | 44篇 |
1980年 | 34篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 36篇 |
1976年 | 36篇 |
1974年 | 22篇 |
1973年 | 38篇 |
1972年 | 23篇 |
排序方式: 共有5570条查询结果,搜索用时 15 毫秒
31.
Ken-ichi Takita Akira Tanigami Takashi Tokino Carol Jones Yusuke Nakamura 《Genomics》1992,13(4):1296-1299
Fifty-four clones containing human inserts were selected from a cosmid library constructed from a somatic cell hybrid containing chromosome 11p15.3-p15.5 as its only human complement. In 32 of these clones, 63 polymorphic systems were identified with a panel of restriction enzymes: 57 conventional RFLP systems and 6 highly polymorphic VNTR systems. Although we examined the cosmid with only seven enzymes, 18 clones (including 6 VNTRs) were polymorphic with three or more enzymes. The results suggested that DNA sequences on the peritelomeric region of chromosome 11p tend to be highly variable. Because these markers are highly informative, they will be excellent resources for investigations of hereditary diseases and tumor suppressor genes in this region of chromosome 11. 相似文献
32.
33.
A micropropagation system was developed to test concepts for automation and microenvironment alteration. Amelanchier x grandiflora Rehd. Princess Diana (serviceberry) shoot cultures were grown in seven-liter polycarbonate containers. Through computer control, the apparatus intermittently applied culture medium to the plant material according to a selected schedule. Shoot growth in the programmable system was compared with four micropropagation treatments: gelled and liquid medium in baby food jars and gelled and non-cycling liquid medium in a seven-liter vessel. Plants cultured in continuous contact with liquid medium became increasingly vitrified. Significantly greater shoot number, shoot length, shoot weight, and culture weight occurred in the programmable system than in jars with gelled medium. The combination of liquid medium, 7-liter vessel, and intermittent contact with medium caused a significantly higher proliferation rate than any combination of jar/vessel and gelled/liquid medium tested. 相似文献
34.
Seed morphology was studied in 15 species of four subgenera ofJuncus occurring in Kansas, to determine if seeds provide traits useful in assessing systematic relations within the genus. In this study seed size and shape were of limited value, while surface ornamentation of the hard inner seed coat provided encouraging results. SubgenusPoiophylli showed little variation in surface ornamentation among taxa; similar ornamentation was observed in subgenusGenuini. SubgeneraGraminifolii andSeptati were separately distinct with the taxa in theSeptati forming a continuum of variation. 相似文献
35.
36.
Stuart Brody Carol Dieckmann Steve Mikolajczyk 《Molecular & general genetics : MGG》1985,200(1):155-161
Summary Five oligomycin-resistant (oli
r) mutant strains of Neurospora crassa were analyzed for their growth rate and for the periodicity of their circadian rhythm. The most resistant strains had periods of 18–19 h while the least resistant strain had a normal period of 21.0 h. There was a rough correlation between the in vivo degree of oligomycinresistance and the amount of change in the period. Several of the oli
r mutations have been previously described by Sebald et al. (1977) in terms of known amino acid changes in the primary structure of the proteolipid, or DCCD-binding protein, found in the F0 membrane portion of the mitochondrial ATP synthetase. Amino acid changes in the structure of this protein are reported here for two other oli
r mutations. The proteolipid isolation procedures were slightly modified to include a delipidation step, and an HPLC procedure was developed to separate the hydrophobic peptides of this protein. Analysis of heterocaryons carrying both the oli
r and oli
s markers indicated that the oli
r and oli
s mutations were codominant to each other in terms of period and growth rate. The changes in the primary structure of this DCCD-binding protein reported here are the first known examples of changes in the primary structure of a protein which alter the period of a circadian rhythm. 相似文献
37.
Summary A histochemical account is presented of the changes that occur in the protein—carbohydrate composition of the cumulus—oocyte complex in immature mice after gonadotrophin treatment. The distribution and nature of the glycosaminoglycans (GAG) present was established by enzymic digestion of tissue sections with testicular orStreptomyces hyaluronidase prior to staining with periodic—acid Schiff (PAS) or Alcian Blue. Treatment with exogenous gonadotrophins [pregnant mare's serum and human chorionic gonadotrophin (hCG)] induced gross changes in the appearance of the zona pellucida (and in the histochemical staining of the cumulus—oocyte complex). A reduction was observed in the amount of PAS-positive material present within the zona pellucida of oocytes located in large Graafian follicles examined 40 h after stimulation with pregnant mare's serum. After the injection of hCG, the zona pellucida was further depleted of PAS-positive naterial. Most of the PAS-positive material became confined to the plasma membrane of the oocyte, while the oocyte itself also became increasingly PAS-positive. All the GAGs disappeared from zona pellucida within 4 h of hCG stimulation. The changes observed in the protein—carbohydrate composition of the zona pellucida in preovulatory oocytes immediately prior to ovulation may be a prerequisite for successful sperm-egg interactions. 相似文献
38.
Ewa Nizankowska Angelita Q. Sheridan Marie H. Maile Carol J. Cross Rafal Nizankowski Krystyna Prochowska Andrew Szczeklik 《Prostaglandins & other lipid mediators》1985,29(3):349-362
We evaluated in a double-blind study the bronchodilatory properties of 2-decarboxy-2-hydroxymethyl prostaglandin E1 (PGE1-carbinol), described recently as a nonirritant bronchodilator in animals. Fifteen asthmatic patients received by inhalation single doses of 1, 10, and 30 μg PGE1-carbinol, 55 μg PGE2, and placebo (10% ethanol in normal saline, which was also used as diluent for the PGs). Such pulmonary function tests as forced expiratory volume in 1 second, forced vital capacity, and maximal expiratory flow were monitored during 2 hours following inhalation of each compound. 10 and 30 μg PGE1-carbinol produced significant but short-acting bronchodilation, similar to that caused by 55 μg PGE2. One-third of the patients reported mild cough and throat irritation during and shortly after inhalation of 30 μg PGE1-carbinol or 55 μg PGE2. Placebo and 1 μg PGE1-carbinol produced minimal side effects, but neither agent caused bronchodilation. In an adjunctive, unblinded trial, the same patients received 400 μg fenoterol. Fenoterol caused greater bronchodilation 15 and 30 minutes after inhalation than did the PGs in the double-blind study. 相似文献
39.
Carol Burck James A. Shapiro Bernhard Hauer 《Molecular & general genetics : MGG》1984,194(1-2):340-342
Summary A pCM2 replicon derived by an N– deletion from ::Tn9 which carries the imm434 immunity region is incompatible with some (but not all) IncP-1 plasmids. The imm pCM1 replicon does not show the same incompatibility behavior. 相似文献
40.