全文获取类型
收费全文 | 64095篇 |
免费 | 5863篇 |
国内免费 | 36篇 |
出版年
2022年 | 396篇 |
2021年 | 920篇 |
2020年 | 566篇 |
2019年 | 694篇 |
2018年 | 866篇 |
2017年 | 818篇 |
2016年 | 1366篇 |
2015年 | 2292篇 |
2014年 | 2536篇 |
2013年 | 3259篇 |
2012年 | 4222篇 |
2011年 | 4310篇 |
2010年 | 2803篇 |
2009年 | 2545篇 |
2008年 | 3566篇 |
2007年 | 3762篇 |
2006年 | 3550篇 |
2005年 | 3434篇 |
2004年 | 3377篇 |
2003年 | 3215篇 |
2002年 | 3082篇 |
2001年 | 699篇 |
2000年 | 558篇 |
1999年 | 809篇 |
1998年 | 970篇 |
1997年 | 703篇 |
1996年 | 627篇 |
1995年 | 569篇 |
1994年 | 559篇 |
1993年 | 581篇 |
1992年 | 606篇 |
1991年 | 503篇 |
1990年 | 509篇 |
1989年 | 487篇 |
1988年 | 470篇 |
1987年 | 412篇 |
1986年 | 435篇 |
1985年 | 467篇 |
1984年 | 573篇 |
1983年 | 461篇 |
1982年 | 590篇 |
1981年 | 598篇 |
1980年 | 482篇 |
1979年 | 371篇 |
1978年 | 397篇 |
1977年 | 354篇 |
1976年 | 388篇 |
1975年 | 265篇 |
1974年 | 328篇 |
1973年 | 311篇 |
排序方式: 共有10000条查询结果,搜索用时 83 毫秒
81.
82.
The computer program HYLAS generates from a standard DNA lettersequence a three-dimensional space curve (H curve) which embodiesthe entire information content of the original nucleotide sequence.The program can display H curves either as two-dimensional (frontand side view) projections or as stereo-pair images. The curvescan be marked at specific nucleotide locations, annotated, rotatedfor observation from any viewing angle, and manipulated forconvenient side-by-side comparisons. Unlike the cumbersome lettersequences, H curves can be drastically condensed in size withoutlosing their ability to reflect the global nucleotide-distributionpattern of the entire DNA sequence. Often, biologically importantloci can be visually identified on the H curves. HYLAS is writtenin FORTRAN with separate mainframe (IBM- VM/CMS) and microcomputer(MS-DOS) versions. It uses the Tektronix-TCS library of graphicsubroutines.
Received on October 24, 1988; accepted on July 15, 1989 相似文献
83.
Ratul Saha Robert S. Donofrio Susan T. Bagley 《Journal of industrial microbiology & biotechnology》2010,37(8):843-848
A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of
three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms
of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since
they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but
are also time-consuming. The primer–probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both
whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 101 colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer–probe pair was successful in determining
concentrations from used MWF samples, indicating levels between 2.9 × 103 and 3.9 × 106 CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 × 101 to 1.4 × 105 CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer–probe pair can be efficiently
used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs. 相似文献
84.
85.
86.
Theodore Page Charles Sherwood James D. Connor Thomas Tarnowski 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,675(2):342
A fast, simple, and cost-effective HPLC method for the quantitation of the antiviral drug ganciclovir is described. The serum samples are extracted with perchloric acid and neutralized with potassium phosphate buffer, and urine samples are diluted with distilled water. A reversed-phase column with isocratic elution by 15 mM potassium phosphate buffer (pH 2.5) containing 0.25% acetonitrile is used to separate ganciclovir; quantitation is by UV absorbance at 254 nm. Total turnaround time is 22 min; more than 3000 samples can be run on a single column without loss of peak quality. The limit of quantitation is 0.05 μg/ml. Recoveries varied from 91 to 10% with coefficients of variation ranging from 0.387 to 7.95%. 相似文献
87.
Background
While traditional models of Alzheimer's disease focused on large fibrillar deposits of the Aβ42 amyloid peptide in the brain, recent work suggests that the major pathogenic effects may be attributed to SDS-stable oligomers of Aβ42. These Aβ42 oligomers represent a rational target for therapeutic intervention, yet factors governing their assembly are poorly understood. 相似文献88.
89.
James McNaught Inglis 《BMJ (Clinical research ed.)》1950,2(4686):1003-1004
90.
Frank Melzner John W. Forsythe James B. Wood Catriona Clemmesen 《Journal of experimental marine biology and ecology》2005,317(1):37-51
A laboratory calibration study was undertaken with juvenile Sepia officinalis (80-85 g initial wet weight) to investigate the effects of different food rations and different starving intervals on RNA/dry weight (DW) ratios and RNA/DNA ratios in cephalopod mantle muscle at two different temperatures. The digestive gland index was also used as an additional indicator of recent growth. High food rations and low temperature went along with high RNA/DW ratios and high RNA/DNA ratios. Starving resulted in a linear decline in growth performance and a concomitant decrease in RNA/DW and RNA/DNA ratio, with RNA/DNA ratios representing the growth data better. RNA/DNA ratios decreased faster at higher temperatures. A fluorimetric assay for nucleic acid analysis was optimized for cephalopod mantle tissues and yielded reproducible RNA/DNA ratios with a relative variance below 10%. Thus, it may be possible to use this estimator of recently encountered feeding regime for the evaluation of mortality rates of early teuthid paralarvae to eventually support stock management. Also, log relative digestive gland weight showed a strong relationship with starving time, but, surprisingly, not with temperature. Data from the two temperatures analyzed could be combined to form a common regression line of relative digestive gland index with starving time. This indicator for recent growth might be especially suitable for large specimens with a well-developed digestive gland. 相似文献