全文获取类型
收费全文 | 54283篇 |
免费 | 4465篇 |
国内免费 | 10篇 |
出版年
2023年 | 247篇 |
2021年 | 416篇 |
2020年 | 366篇 |
2019年 | 356篇 |
2018年 | 1039篇 |
2017年 | 1095篇 |
2016年 | 1242篇 |
2015年 | 1212篇 |
2014年 | 1413篇 |
2013年 | 2363篇 |
2012年 | 3766篇 |
2011年 | 4153篇 |
2010年 | 2172篇 |
2009年 | 1513篇 |
2008年 | 3401篇 |
2007年 | 3483篇 |
2006年 | 3240篇 |
2005年 | 2950篇 |
2004年 | 2774篇 |
2003年 | 2594篇 |
2002年 | 2545篇 |
2001年 | 1640篇 |
2000年 | 1889篇 |
1999年 | 1041篇 |
1998年 | 508篇 |
1997年 | 403篇 |
1996年 | 472篇 |
1995年 | 409篇 |
1994年 | 424篇 |
1993年 | 388篇 |
1992年 | 454篇 |
1991年 | 394篇 |
1990年 | 330篇 |
1989年 | 349篇 |
1988年 | 324篇 |
1987年 | 314篇 |
1986年 | 272篇 |
1985年 | 375篇 |
1984年 | 435篇 |
1983年 | 388篇 |
1982年 | 359篇 |
1981年 | 347篇 |
1980年 | 301篇 |
1979年 | 301篇 |
1978年 | 309篇 |
1977年 | 280篇 |
1976年 | 295篇 |
1975年 | 336篇 |
1974年 | 272篇 |
1973年 | 238篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Barna Györffy 《Planta》1941,32(1):15-37
Zusammenfassung In der Mehrzahl der untersuchten Fälle (insgesamt über 1000 Einzelmessungen) wurden die osmotischen Werte der Tetraploiden niedriger gefunden als die der Diploiden, doch sind die Unterschiede im allgemeinen gering. Junge Pflanzen hatten immer niedrigere 4n-Werte; bei alten Pflanzen und bei Pflanzen unter extremen Kulturbedingungen waren aber vielfach die Werte der 4n höher. Es wird die Hypothese aufgestellt, daß niedrigere osmotische Werte der Tetraploiden den Normalzustand darstellen, daß aber die Polyploiden wie in anderen Eigenschaften, so auch in ihrer Osmotik variabler sind und unter dem Einfluß von Außen-bedingungen ihre osmotischen Werte stärker modifizieren.Unter physiologischen Zwangsbedingungen (Trockenkultur, Pfropfungen) wurde an den Tetraploiden eine unter den gegebenen Verhältnissen zweckmäßige Erhöhung ihrer osmotischen Werte über das Niveau der 2n beobachtet. Gegen Trockenklima erwiesen sich die untersuchten Tetraploiden im Vergleich mit den Diploiden resistenter.Irgendwelche artspezifischen Eigentümlichkeiten konnten im Rahmen der untersuchten Pflanzen nicht festgestellt werden.Mit 6 Textabbildungen. 相似文献
62.
For some foodstuffs, determination of the mycotoxin ochratoxin A (OTA) requires time consuming clean up by means of solid
phase extraction (SPE). Therefore a system for automated SPE was tested for cleaning up roasted coffee as a possible way of
shortening preparation time. Validation of the method in accordance to the so called “Concept '98” led to a LOD of 0.2 μg/kg
and a recovery rate of 92%. By using the described procedure with samples of roasted coffee the OTA contents varied between
the LOD and 3.4 μg/kg. This method was also used to determine ochratoxin A in liquorice roots, ginger and valerian.
Presented at the 26th Mykotoxin Workshop in Herrsching, Germany, May 17–19, 2004 相似文献
63.
64.
Hubert L. Dulieu 《Mutation research》1974,25(3):289-304
A greenish-yellow mutant was obtained after treatment of seeds of Nicotiana tabacum L. var. Xanthi n.c. with ethyl methanesulfonate (EMS). Two genetically independent mutations (a1 and a2) were isolated. The first mutation (a1) antagonizes the function of its partially dominant a1+ allele. The second mutation (a2) is amorphous but strongly interacts with a1.Among the nine possible genotypes at the two loci, five varied in somatic cells. The heterozygous state a1+/a1 strongly increased the frequency of both spontaneous and induced variations. However, two homozygotes also showed variations.Variants were isolated from induced and spontaneous non-reciprocal and reciprocal variations within paliside tissues by bud induction in vitro. They were genetically tested. In this first paper, only non-reciprocal variations are reported.Green variants from the greenish-yellow (J1) dihybrid a1+/a1a2+/a2 clone had two genotypes: the first was due to true reversions of a1 to a1+, whereas the second was due to amorphous a10 mutations from a1. These a10 mutations may well be deletions.The lightest yellow variants from J1 were due to mutations either from a1+ into a1 or from a2+ into a2.Deletions at the a1+?a1 locus led to either yellow variations when a1+ was lost, or to false reversions when the antagonistic allele a1 was lost.Amorphous alleles at the a1+?a1 locus were also isolated from tissues other than J+. They gave zygotic lethality (s) that probably varied with the size of the deletions. Thus, true reversions and deletions at the a1+?a1 locus could be distinguished from one another by progeny tests.Other variants showed higher frequencies of spontaneous variations (instability). Somatic changes observed in these unstable systems were due to modifications at the marker loci. The genetic nature of this instability is not yet known.There is strong evidence that the genetic events involved in these non-reciprocal variations were deletions, conversions and point mutations. True reversions from a1 into a1+ and new mutations from a1+ into a1 were obtained only from a1+/a1. It was therefore supposed that the changes observed took place only in heterozygotes, and the conversion hypothesis was made. Attempts are being made to prove that conversions do exist in higher plants, and to find out if this process, as deletions, is induced by radiation. 相似文献
65.
66.
67.
68.
HAROLD St. JOHN F.L.S. 《Biological journal of the Linnean Society. Linnean Society of London》1972,4(4):305-310
Sydney Parkinson, aged 18, was Sir Joseph Banks' private assistant and artist on Captain Cook's first voyage around the world. Parkinson died on the voyage. Among his effects delivered to his brother Stanfield were drawings and notes which the latter published as a journal. Included in it is a chapter on the economic plants of Tahiti, and most of them are given scientific names, some of which were new. In 1941 Fosberg adopted two of them to form names which were new combinations under Artocarpus , and Inocarpus . The writer now indicates that Parkinson's names of 1773 were mononomials, hence invalid, but that in the German edition of 1774, edited by Herr "Z", the names are valid binomials. For the two plants mentioned, the authorship of the combinations is revised. 相似文献
69.
70.