全文获取类型
收费全文 | 2386篇 |
免费 | 219篇 |
国内免费 | 1篇 |
出版年
2021年 | 28篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 34篇 |
2015年 | 49篇 |
2014年 | 76篇 |
2013年 | 98篇 |
2012年 | 95篇 |
2011年 | 106篇 |
2010年 | 78篇 |
2009年 | 63篇 |
2008年 | 86篇 |
2007年 | 121篇 |
2006年 | 90篇 |
2005年 | 78篇 |
2004年 | 100篇 |
2003年 | 79篇 |
2002年 | 68篇 |
2001年 | 72篇 |
2000年 | 85篇 |
1999年 | 69篇 |
1998年 | 30篇 |
1997年 | 23篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1993年 | 24篇 |
1992年 | 37篇 |
1991年 | 56篇 |
1990年 | 53篇 |
1989年 | 40篇 |
1988年 | 34篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 35篇 |
1984年 | 33篇 |
1983年 | 34篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 31篇 |
1976年 | 35篇 |
1975年 | 41篇 |
1974年 | 26篇 |
1973年 | 31篇 |
1972年 | 21篇 |
1971年 | 20篇 |
1970年 | 20篇 |
1969年 | 24篇 |
1967年 | 18篇 |
排序方式: 共有2606条查询结果,搜索用时 31 毫秒
21.
Comparison of a new inorganic membrane filter (Anopore) with a track-etched polycarbonate membrane filter (Nuclepore) for direct counting of bacteria. 总被引:4,自引:3,他引:1 下载免费PDF全文
Bacterial counts obtained by using a new Anopore inorganic membrane filter were 21 to 33% higher than those obtained by using a Nuclepore polycarbonate membrane filter. In addition, the inorganic filter had higher flow rates, permitting lower vacuum pressures to be used, while the intrinsically flat, rigid surface resulted in easier focusing and sharp definition of bacteria across the whole field of view. 相似文献
22.
23.
Regulation of gene expression in rat prostate by androgen and beta-adrenergic receptor pathways 总被引:1,自引:0,他引:1
P D Guthrie M R Freeman S T Liao L W Chung 《Molecular endocrinology (Baltimore, Md.)》1990,4(9):1343-1353
Denervation of rat ventral prostate has been accomplished by excising prostatic tissue fragments and implanting them under the renal capsules of intact syngeneic rats. This resulted in a substantial reduction of expression of a major organ-specific secretory protein, prostatic binding protein (PBP). The depressed level of PBP and its subunits and mRNAs could be restored, however, to as much as 80% of control levels by the administration of a pharmacological dose of exogenous androgen, testosterone propionate (TP), and/or a beta-adrenergic agonist, isoproterenol (ISO). Furthermore, compared to ascorbate-treated controls, TP and ISO increased the synthesis of total cellular protein and PBP by the prostatic renal implants. TP and/or ISO also remodelled the luminal epithelial structure and elevated secretory functions. ISO alone had no effect, however, in castrated animals, indicating that androgen plays a dominant role in the restoration of tissue PBP content. Concomitant to increased PBP content and remodelling of prostatic histomorphology, androgen was also found to raise the depressed levels of beta 2-adrenergic and androgen receptors in the prostatic isografts maintained in intact hosts. In contrast, although an established rat prostatic epithelial cell line (NbE-1) contains high affinity androgen receptor, androgen failed to restore beta-adrenergic receptor as well as PBP content in this cultured cell line. These results, taken together, suggest that a tight coupling between androgen receptor and beta 2-adrenergic receptor pathways may be a prerequisite for PBP expression and functional differentiation in the rat ventral prostate gland. 相似文献
24.
Summary A continuous non-aerated process for the 1 of hydrocortisone by gel-entrapped Arthrobacter simplex was developed. The process employs PAAH-bead entrapped cells for the continuous conversion of up to 1.6 g/l hydrocortisone solutions in cosolvent containing buffer. Employing ethyleneglycol (10–20% (v/v)) as the cosolvent of choice and menadione sodium bisulfite as effective, non-toxic, sole electron acceptor, efficient non-aerated continuous production of prednisolone in a packed bed conlumn could be maintained, at least for the 30–40 day period of continuous operation tested. The high operational stability observed was made possible by the combined effect of immobilization technique (PAAH bead entrapment), wisely selected cosolvent and artificial electron acceptor, and elimination of aeration and vigorous mixing. 相似文献
25.
Many patients with suspected colonic disease undergo rigid sigmoidoscopy, barium enema examination, and ultimately total colonoscopy, but the need for preliminary radiology has not been formally assessed. A total of 168 patients requiring large bowel investigation were therefore randomised to undergo either rigid sigmoidoscopy plus double contrast barium enema examination or total colonoscopy. Disease was found in 56 patients, including 14 with a carcinoma, 11 with polyps, and 16 with inflammatory bowel disease, the remainder having diverticular disease alone. Of the 89 patients allocated to double contrast barium enema examination, nine required a subsequent colonoscopy for suspected tumour or polyps, three because of incomplete radiological examination, and 12 for rectal bleeding for which no cause was found at the radiological examination. In 16 patients this yielded further information or altered treatment. Of the 79 patients undergoing total colonoscopy, only six required subsequent radiology.As both procedures were well tolerated with no major complications total colonoscopy may be the preferred initial investigation where facilities allow. 相似文献
26.
27.
28.
N Uchida R D Cone G J Freeman R C Mulligan H Cantor 《Journal of immunology (Baltimore, Md. : 1950)》1986,136(5):1876-1879
To establish a gene transfer and expression system for murine T cell clones, we have introduced the neomycin phosphotransferase gene encoding resistance to the neomycin analogue, G418, into non-neoplastic inducer T cell clones by using a replication-defective retroviral vector. This method allowed highly efficient gene transfer (20 to 40%) into two inducer T cell clones. The level of viral RNA expression in G418r T cells was 0.1% of poly(A)+ RNA. The infected G418r cells retained physiologic responsiveness to specific antigen as judged by antigen-specific proliferation and production of IL 3. 相似文献
29.
Monoamine Neurotransmitter Metabolism and Locomotor Activity During Chemical Hypoxia 总被引:4,自引:1,他引:3
The effects of hypoxia on metabolism of 5-hydroxytryptamine (5-HT or serotonin) and 3,4-dihydroxyphenylethylamine (DA or dopamine) were compared with those on open-field activity in male CD-1 mice. Chemical hypoxia was induced with NaNO2. Hypoxia did not alter striatal concentrations of DA, 5HT, Trp, Tyr, 5-hydroxyindoleacetic acid, or homovanillic acid. However, NaNO2 (75 mg/kg) reduced the rates of conversion of [3H]Tyr to [3H]DA (-41%) and [3H]Trp to [3H]5-HT (-39%). Hypoxia also reduced dihydroxyphenylacetic acid (DOPAC) levels (-27%) and DOPAC/DA ratios (-20%). Open-field behavior, as measured in an automated activity monitor, decreased in a dose-dependent fashion with 75-150 mg/kg of NaNO2 (-35 to -90%). Comparison with previous studies suggests that the syntheses of dopamine, serotonin, and the amino acids are equally vulnerable to hypoxic insults but may be less sensitive than the synthesis of acetylcholine. 相似文献
30.
Freshly isolated human lymphocytes were used to determine how serum supplements affect cellular capacity to repair UV damage. Repair capacity was always found to be greatest in medium supplemented with autologous plasma. Variability in repair capacity among individuals was greater in serum supplemented medium than in unsupplemented medium. Thus, in vitro cellular responses will most accurately represent in vivo responses if autologous serum factors are present in the culture medium. This is of particular importance in studies attempting to correlate DNA repair capacity with age or susceptibility to carcinogenesis. 相似文献