全文获取类型
收费全文 | 1650篇 |
免费 | 133篇 |
国内免费 | 1篇 |
出版年
2021年 | 32篇 |
2020年 | 24篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 40篇 |
2015年 | 71篇 |
2014年 | 84篇 |
2013年 | 105篇 |
2012年 | 111篇 |
2011年 | 97篇 |
2010年 | 89篇 |
2009年 | 79篇 |
2008年 | 109篇 |
2007年 | 102篇 |
2006年 | 85篇 |
2005年 | 85篇 |
2004年 | 79篇 |
2003年 | 81篇 |
2002年 | 53篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1965年 | 7篇 |
1962年 | 6篇 |
1956年 | 6篇 |
1936年 | 5篇 |
1927年 | 7篇 |
1920年 | 5篇 |
1908年 | 5篇 |
排序方式: 共有1784条查询结果,搜索用时 656 毫秒
1.
2.
3.
Kluyveromyces lactis CBS 683, showed no Crabtree effect but the Pasteur effect was very strong. It could be seen that the metabolism of glucose was adaptative. The anaerobic fermentation of lactose was always greater than the anaerobic fermentation on glucose and galactose. The transport across wall and cell membrane of glucose and galactose limits the fermentation rate of these substrates. 相似文献
4.
G C du Moulin E C Coleman J Hedley-Whyte 《Applied and environmental microbiology》1987,53(6):1322-1326
We measured endotoxin and bacterial levels in tap water, in water purified by reverse osmosis, and in dialysate samples over a 4-month period in a new 10-bed renal dialysis unit. Water treated by reverse osmosis is conducted to the 10 stations through 111 m of piping composed of acrylonitrile butadiene styrene (ABS). All determinations were made prior to the opening of the unit and after the system was purged for 35 h with all bedside station taps open. Formaldehyde disinfection of the piping system was attempted with a recommended protocol after 11 weeks by feeding 2.5 liters of 37% formaldehyde (0.85%, vol/vol) into the delivery system. Prior to water purging, 24 ng of endotoxin per ml was detected. This level decreased to 2.0 ng of endotoxin after the purging. Levels of endotoxin remained below 1.0 ng of endotoxin per ml throughout the duration of the study. In contrast, the level of viable microorganisms recovered from the treated water was approximately 3.5 X 10(4) CFU/100 ml. Even after disinfection of the system, there was no significant decrease in culturable bacteria from the water even though endotoxin levels were lower. Species isolated from the renal dialysis system were predominately pseudomonads, whereas species isolated from the tap water were Bacillus and Flavobacterium species. ABS provides a surface suitable for long-term colonization and growth of bacteria. Currently recommended decontamination protocols are ineffective in removing potentially pathogenic bacteria from ABS pipes and thus constitute an increased risk to patients undergoing dialysis. 相似文献
5.
Kazimierz S. Kasprzak Michael P. Waalkes Lionel A. Poirier 《Biological trace element research》1987,13(1):253-273
Interactions between the physiologically essential metals calcium, magnesium, and zinc and the carcinogenic metals nickel
and cadmium were investigated to help elucidate the mechanisms of action of the carcinogenic metals. Bioassay studies revealed
several significant findings, including: (1) the ability of magnesium and calcium to inhibit nickel-induced elevation of pulmonary
adenoma incidence in strain A mice; (2) the ability of magnesium, but not of calcium, to prevent cadmium-induced subcutaneous
sarcoma formation; and (3) the ability of magnesium, but not of calcium, to inhibit nickel-induced muscle tumor formation.
Biochemical studies indicated a direct relationship between the antitumorigenic potential of magnesium and the capacity of
this metal to: (1) inhibit nickel and cadmium uptake by the target tissues in vivo; (2) inhibit nickel-induced disturbances
in DNA synthesis in vivo; (3) inhibit nuclear and cytosolic uptake of nickel by the target tissue cells in vivo; and (4) inhibit
nickel and cadmium binding to DNA in vitro. Calcium, which in most cases did not prevent carcinogenesis, had no consistent
influence on the uptake of carcinogenic metals or their biochemical effects in the target tissues. Magnesium and zinc, but
not calcium, were also found to attenuate the acute toxic effects of nickel, indicating a possible correlation between prevention
of acute effects and reduction in tumorigenicity. Zinc, which antagonizes cadmium tumorigenicity in the rat testis, was found
to reduce markedly cadmium uptake into isolated testicular interstitial cells. Also, zinc was found to inhibit strongly cadmium
binding to DNA in vitro. 相似文献
6.
Transport of lactose intoKluyveromyces lactis was accomplished by a highly specific system inducible by lactose and galactose. The biosynthesis of the transport enzyme
was strongly repressed by glucose. For non-induced cells, lactose penetrated by passive transport, like galactose in any type
of cells. The lactose transport showed aK
m 1.2 –4 mm, was temperature-dependent (76 kJ/mol) and was blocked by metabolic inhibitors. 相似文献
7.
Study of the lactose and galactose transport systems in Kluyveromyces lactis has shown that lactose uptake is by active transport. The transport system is under monogenic control and is inducible. Galactose uptake is also by active transport but the system is controlled by two genes which, in the four strains we studied, are present only in K. lactis CBS 2359. Galactose uptake in the other K. lactis strains is by a simple diffusion process. 相似文献
8.
Ola Palm W. Lionel Weerakoon M. Ananda P. de Silva Thomas Rosswall 《Plant and Soil》1988,108(2):201-209
Sesbania sesban was evaluated as green manure crop for lowland rice in the Dry Zone of Sri Lanka. The legume was grown during a fallow period
before lowland rice (Oryza sativa) and ploughed under just before transplanting. Weight loss and nitrogen content in litterbags containing leaves, stems and
roots of the legume were monitored. Comparisons were made between rice yields from 20 m2 plots after green manuring in combination with different nitrogen fertilizer levels (0, 2.4, 4.8 and 7.2 gm−2) and nitrogen fertilizer (9.6 gm−2) alone. Above-ground biomass ofS. sesban was 440 gm−2 (dry wt) when ploughed under after 84 days growth. N-content in leaves, stems and roots was 3.76%, 0.41% and 0.73%, respectively.
This gave a N-input fromS. sesban of 9.2 gm−2 (8.3 g from above-ground parts and 0.9 g from roots). The corresponding K and P inputs were 7.3 and 0.6 gm−2 respectively. The nitrogen rich leaves, which contained 88% of the nitrogen in the above-ground parts, decomposed and released
its nitrogen much more rapidly than the stems and roots. After only four days the leaves had released 5.3 g Nm−2 and after 14 days they had released 6.4 g Nm−2. The highest rice yield (505 gm−2) was obtained usingS. sesban and 4.8 gm−2 of N-fertilizer. The yields with only N-fertilizer or onlyS. sesban were 442 gm−2 and 396 gm−2, respectively. Due to the rapid decomposition of the nitrogen rich leaves,S. sesban did not behave as a slow release fertilizer. Thus, it is not necessary to apply nitrogen fertilizers as a basal dose. 相似文献
9.
D E Moulin N G Johnson N Murray-Parsons M F Geoghegan V A Goodwin M A Chester 《CMAJ》1992,146(6):891-897
OBJECTIVE: To provide guidelines for the institution and maintenance of a continuous subcutaneous narcotic infusion program for cancer patients with chronic pain through an analysis of the narcotic requirements and treatment outcomes of patients who underwent such therapy and a comparison of the costs of two commonly used infusion systems. DESIGN: Retrospective study. SETTING: Tertiary care facilities and patients'' homes. PATIENTS: Of 481 patients seen in consultation for cancer pain between July 1987 and April 1990, 60 (12%) met the eligibility criteria (i.e., standard medical management had failed, and they had adequate supervision at home). INTERVENTION: Continuous subcutaneous infusion with hydromorphone hydrochloride or morphine started on an inpatient basis and continued at home whenever possible. OUTCOME MEASURES: Patient selectivity, narcotic dosing requirements, discharge rate, patient preference for analgesic regimen, side effects, complications and cost-effectiveness. RESULTS: The mean initial maintenance infusion dose after dose titration was almost three times higher than the dose required before infusion (hydromorphone or equivalent 6.2 v. 2.1 mg/h). Eighteen patients died, and the remaining 42 were discharged home for a mean of 94.4 (standard deviation 128.3) days (extremes 12 and 741 days). The mean maximum infusion rate was 24.1 mg/h (extremes 0.5 and 180 mg/h). All but one of the patients preferred the infusion system to their previous oral analgesic regimen. Despite major dose escalations nausea and vomiting were well controlled in all cases. Twelve patients (20%) experienced serious systemic toxic effects or complications; six became encephalopathic, which necessitated dose reduction, five had a subcutaneous infection necessitating antibiotic treatment, and one had respiratory depression. The programmable computerized infusion pump was found to be more cost-effective than the disposable infusion device after a break-even point of 8 months. CONCLUSIONS: Continuous subcutaneous infusion of opioid drugs with the use of a portable programmable pump is safe and effective in selected patients who have failed to respond to standard medical treatment of their cancer pain. Dose titration may require rapid dose escalation, but this is usually well tolerated. For most communities embarking on such a program a programmable infusion system will be more cost-effective than a disposable system. 相似文献
10.